A microservice is an architectural style, in which complex applications are composed of small, independent processes communicating with each other using language-agnostic APIs - wikipedia 
It is an approach to developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API. - martinfowler.com
# See also
- Fallacies of Distributed Computing
- Microservices not a free lunch - highscalability.com
- Microservices
- Serverless Microservices