What does the ENTRYPOINT instruction do in a Dockerfile?

The ENTRYPOINT instruction in a Dockerfile is used to specify the command that will be executed when a container is run from the image. It allows you to configure a container to run as an executable.

There are two forms of the ENTRYPOINT instruction:

Exec form (recommended):
```
ENTRYPOINT ["executable", "param1", "param2"]
```
This form does not invoke a shell, and the command is executed directly. It is more efficient and allows for better signal handling.
Shell form:
```
ENTRYPOINT command param1 param2
```
This form runs the command in a shell (/bin/sh -c), which can be useful for shell features but may lead to issues with signal handling.

Using ENTRYPOINT allows you to define a default behavior for your container, which can be overridden by providing additional command-line arguments when running the container.