Block
Definitions
The Edge Delivery Services realization of a Component Contract — EDS's own nomenclature
What AEM calls a Component, EDS calls a Block. Using "component" for one is a category error on that platform.
A deployable artifact: one directory, <slug>/<slug>.js and <slug>.css, following Adobe's convention so it can be dropped into an aem.live repository as-is
The build-side sense, used where Blocks are generated and vendored. A host project's fragment stand-in module is not a Block, even though it lives beside them.
One word, two vantage points. From the design system, a Block is the EDS realization of a Component Contract — the counterpart of an AEM Component. From the build, a Block is a directory you can hand to an aem.live site. They are the same referent seen from the contract side and the artifact side, which is why one entry carries both.
Avoid: Component, which is the AEM term; and calling a host's fragment module a Block — it is a stand-in for the host's own, marked external so the specifier survives the build.