So I took a step back and tried to think about why one "feels" to a reader more like a definition than the other. I think it comes down to phrasing more than informational content. The definition you provide in your comment comes off, for lack of a better term, too much like a sales pitch.
Less is more when it comes to definitions, at least for defining terms in articles/blog posts like these.
Here's my attempt at a better (for this use case) definition:
A semantic layer is an interface to data stores that is designed to be queryable in terms relevant and familiar to those with knowledge of the business domain.