As others have mentioned, it‘s an import rename. There is however one further feature that proves astoundingly-useful on occasion that I would like to highlight: If you "rename" to _, the symbol is no longer imported.
This is useful in a few cases. The simplest is that you‘d like to do a wildcard import from two packages, but there‘s a name that‘s defined in both and you‘re only interested in one of them:
import java.io.{ File=>_, _ }
import somelibrary._Now when you reference File, it will unambiguously use the somelibrary.File without having to fully-qualify it.
In that case, you could have also renamed java.io.File to another name to get it out of the way, but sometimes you really do not want a name visible at all. This is the case for packages that contain implicits. If you do not want a particular implicit conversion (e.g. if you‘d rather have a compile error) then you have to delete its name completely:
import somelibrary.{RichFile => _, _}
// Files now won‘t become surprise RichFiles