My understanding is that it's essentially Looker minus the dashboarding. What you would define via LookML is essentially the "semantic layer" that this is addressing. DBT is attempting to do similar work: https://www.getdbt.com/product/semantic-layer/

"Looker minus dashboarding plus APIs (SQL/REST/GraphQL) and, subjectively, better aggregate awareness (AKA "pre-aggregations" in Cube).