"Microservice" describes the size and scope of each deployment artifact. It answers the question "is the whole system just one big ball, is it broken up, how broken up is it?" It doesn't describe how it is deployed.

"Serverless" describes how a deployment artifact is deployed and runs. Generally it refers to a class of technologies in multiple domains whereby intricate knowledge of the underlying host is abstracted behind a cleaner API, with things like scaling, security, patching, etc handled by an infrastructure provider. While the term rose in prominence alongside "functions as a service", which is certainly a technology that generally qualifies as serverless, there are many serverless products out there: AWS Fargate for running containers, DynamoDB for a database, S3 for object storage, all of these are "serverless". A good signal is: if I can SSH into it, its not serverless.

A microservice can certainly be deployed serverless (ECS/Fargate or Google Cloud Run comes to mind). A microservice can even refer to one or more logically related functions-as-a-service; the term more-so speaks to how the engineering teams organize their business domain into the code and how the APIs speak to each other, rather than the exact underlying technologies.