# Nomenclature issue: trimming vs truncation
**URL:** https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101
**Category:** User Support
**Tags:** trim, truncate
**Created:** [October 18, 2021, 7:03pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101 "2021-10-18T19:03:46Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@vheidrich](https://forum.qiime2.org/u/vheidrich)
#### Post date: [October 18, 2021, 7:03pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/1 "2021-10-18T19:03:46Z")
Hi everyone,
After chatting with a collaborator, I am now questioning a little bit my interpretation of the terms _trimming_ and _truncation_. What's the difference between them to you?
My interpretation is that _trimming_ is used when we are removing a fixed number of bases from the reads ends, while _truncation_ is used when we are removing a variable number of bases from the reads ends in order to get an homogeneous set of reads as a result.
For instance, consider the following set of reads:
AAAAAA
AAAAAAAAA
AAAAAAA
i) After _trimming_ 2 last bases
AAAA
AAAAAAA
AAAAA
ii) After _truncation_ at 5th position
AAAAA
AAAAA
AAAAA
That is, when we _trim_ the action is the same for all reads (remove 2); when we _truncate_ the result is the same for all reads (same length). Of course we can get the result observed in (ii) by trimming a variable number of bases per read, so that's maybe another way to think about it: _truncation_ is _trimming_ a variable number of bases per read in order to make the result homogeneous. Is this correct? Am I missing something obvious?
I would also like to ask: does this nomenclature changes somehow when we go from reads to ASVs? Is the way we call it influenced by how "raw" the data is?
Thanks in advance,
Vitor
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### Author:  [@lizgehret](https://forum.qiime2.org/u/lizgehret)
#### Post date: [October 19, 2021, 4:19pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/2 "2021-10-19T16:19:32Z")
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### Author:  [@thermokarst](https://forum.qiime2.org/u/thermokarst)
#### Post date: [November 3, 2021, 1:39pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/3 "2021-11-03T13:39:42Z")
8 off-topic replies have been split into a new topic: [2021-11-03 trimming/trunc question](https://forum.qiime2.org/t/2021-11-03-trimming-trunc-question/21243)
Please keep replies on-topic in the future.
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### Author:  [@lizgehret](https://forum.qiime2.org/u/lizgehret)
#### Post date: [October 19, 2021, 9:57pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/4 "2021-10-19T21:57:01Z")
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### Author:  [@thermokarst](https://forum.qiime2.org/u/thermokarst)
#### Post date: [October 26, 2021, 9:43pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/7 "2021-10-26T21:43:44Z")
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### Author:  [@lizgehret](https://forum.qiime2.org/u/lizgehret)
#### Post date: [October 28, 2021, 6:51pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/10 "2021-10-28T18:51:15Z")
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### Author:  [@vheidrich](https://forum.qiime2.org/u/vheidrich)
#### Post date: [October 18, 2021, 7:03pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/11 "2021-10-18T19:03:46Z")
Hi everyone,
After chatting with a collaborator, I am now questioning a little bit my interpretation of the terms _trimming_ and _truncation_. What's the difference between them to you?
My interpretation is that _trimming_ is used when we are removing a fixed number of bases from the reads ends, while _truncation_ is used when we are removing a variable number of bases from the reads ends in order to get an homogeneous set of reads as a result.
For instance, consider the following set of reads:
AAAAAA
AAAAAAAAA
AAAAAAA
i) After _trimming_ 2 last bases
AAAA
AAAAAAA
AAAAA
ii) After _truncation_ at 5th position
AAAAA
AAAAA
AAAAA
That is, when we _trim_ the action is the same for all reads (remove 2); when we _truncate_ the result is the same for all reads (same length). Of course we can get the result observed in (ii) by trimming a variable number of bases per read, so that's maybe another way to think about it: _truncation_ is _trimming_ a variable number of bases per read in order to make the result homogeneous. Is this correct? Am I missing something obvious?
I would also like to ask: does this nomenclature changes somehow when we go from reads to ASVs? Is the way we call it influenced by how "raw" the data is?
Thanks in advance,
Vitor
---
### Author:  [@lizgehret](https://forum.qiime2.org/u/lizgehret)
#### Post date: [October 19, 2021, 9:56pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/12 "2021-10-19T21:56:50Z")
Hi @vheidrich,
Thanks for reaching out, these are **great** questions! I'll discuss below the differences between trimming and truncating (as they are utilized within the QIIME 2 core framework).
**`Trimming`** : The number of base pairs that will be removed from either the 3' or the 5' end. In QIIME 2, you'll most commonly see **trim-left** (which will trim off the requested number of base pairs from the 5' end), but in `qiime feature-classifier extract-reads`, there is also a **trim-right** parameter, which refers to the 3' end.
**`Truncating`** : The position at which reads will be truncated (counting from the 5' end). Reads that are shorter than the value provided will be discarded. The command you'll see this action represented by within QIIME 2 is **trunc-len**. Something to note is that in the denoising pipelines within the QIIME 2 core framework, truncation occurs before trimming.
Here is an example that may help further clarify - take the following words as sequence examples:
**QIIME2**
**TRIMMING**
**TRUNCATION**
I will first truncate the above sequences with this command:
`trunc-len 7`
This is what I will be left with:
**TRIMMIN**
**TRUNCAT**
Note that QIIME2 was dropped because it is shorter than the truncation of 7 that was specified.
I will now trim the remaining sequences with this command:
`trim-left 2`
This is what I will be left with:
**IMMIN**
**UNCAT**
Hope this helps!
Cheers :qiime2: 🦎
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### Author:  [@vheidrich](https://forum.qiime2.org/u/vheidrich)
#### Post date: [October 19, 2021, 10:20pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/13 "2021-10-19T22:20:36Z")
Hi @lizgehret,
This helps a lot! It is nice that you mentioned that not always the practical meaning of this terms will be the same, so I guess it really depends on the tools we are using. I'll mark your reply as the solution because this answers whether I should say trimming or truncating in a presentation I've been working on.
Thank you very much,
Vitor
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### Author:  [@lizgehret](https://forum.qiime2.org/u/lizgehret)
#### Post date: [October 28, 2021, 6:50pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/16 "2021-10-28T18:50:40Z")
Hi @vheidrich,
I wanted to reach back out because it was brought to my attention that my understanding of trimming vs. truncation wasn't quite correct - I've gone back and modified my original response from above to more accurately reflect how trimming and truncating are used within the QIIME 2 core framework. Apologies for the mix-up on my end!
Cheers 🦎
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### Author:  [@vheidrich](https://forum.qiime2.org/u/vheidrich)
#### Post date: [October 28, 2021, 8:13pm UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/17 "2021-10-28T20:13:21Z")
Hi @lizgehret,
Thank you for the clarification. I guess now your answer is much more in line with my previous notion, but much better explained and the examples really help! We both probably went back and forth into what these terms mean within the QIIME 2 core framework throughout this topic, so definitely evidence that their meanings are not trivial. Hence, I assume this topic will help a lot of other people in the :qiime2: community with similar doubts.
So thanks again!
Vitor
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### Author:  [@system](https://forum.qiime2.org/u/system)
#### Post date: [November 19, 2021, 1:04am UTC](https://forum.qiime2.org/t/nomenclature-issue-trimming-vs-truncation/21101/18 "2021-11-19T01:04:42Z")
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