The Problem of compose in docker from Beginner to Practice?

  docker, question

The following is a description of the book:

There are two important concepts in Compose:
 -service: An application container can actually include several container instances running the same image.
 -project: A complete business unit consisting of a set of associated application containers, defined in the' docker-compose.yml' file.

“Project” is easy to understand. It is made up of multiple containers.
However, the “service” described here is completely incomprehensible. What individuals originally understood was that the service is “a container of applications”. What is itIn fact, it can include several container instances running the same mirror image.?

A service can have multiple container instances

https://docs.docker.com/compo …