The Strangler pattern is one in which an “old” system is put behind an intermediary facade. Then, over time external replacement services for the old system are added behind the facade. The facade represents the functional entry points to the existing system. Calls to the old system pass through the facade. 

Modernize an application by incrementally developing a new (strangler) application around the legacy application. 

In this scenario, the strangler application has a microservice architecture.