What does Maven Update Project do in Eclipse?

I could not dig out the documentaiton, but I was able to dig out the code. To complement @Gimby answer - you can go into details and look into what the function does in here:

https://github.com/eclipse/m2e-core/blob/41f5ae34ad2543ef1439b7fd7e0a03b596af8685/org.eclipse.m2e.core/src/org/eclipse/m2e/core/internal/project/ProjectConfigurationManager.java#L365

Look for : updateProjectConfiguration0 function.

Cheers,