a capital 'M' microservice is a service that is entirely self-contained with its own datastore and everything. It's an architecture that makes sense if you are talking about the 'Orders' component of an e-commerce website but starts to get really weird if you need to share any kind of data between the microservices.
Suddenly something trivial becomes buzzword-filled chaos. Observability, apm, monitoring, kubernetes, scaling, events, pub sub, api contracts, Kafka, streams, multi repos, build pipelines, github workers, eventual consistency and so on.