An ASV is a type of feature but a feature is not a type of ASV. Does that make sense?
This forum post describes the generic term "feature" and why we use it (replacing qiime1-era use of the more specific term "otu" as a general term, e.g., "otu table").
ASV appears on the forum but not the official docs as much because there is a lot of variation over the precise terminology — sequence variant vs. "actual" SV vs. "amplicon" SV vs. "denoised" SV vs. 100% OTU, etc. And while dada2/deblur output sequence variants the rest of QIIME2 is largely agnostic to the types of features contained in feature tables.
I hope that clarifies!