The term “microservice” is used to denote a software system that is narrowly scoped in it’s concern and interest, providing a simple and direct way to interface with that interset.
For example, Vox Media runs a microservice dedicated to associating natural language terms with URL’s in order to automatically create back-links from new stories to older stories — when you see “the playoffs” insert a lin to
sbnation.com/nba-playoffs. This service has an API for creating and managing the phraser/url combinations, as well as an endpoint for finding links inside a given body of text.
In an ideal world, a microservice is completely decoupled from any other part of the system. It neither relies on other services to function, nor prevents other services from functioning if is not available.