What is this Bash (and/or other shell?) construct called?
This is process substitution, as you have been told. I'd just like to point out that this also works in the other direction. Process substitution with >(cmd) allows you to take a command that writes to a file and instead have that output redirected to another command's stdin. It's very useful for inserting something into a pipeline that takes an output filename as an argument. You don't see it as much because pretty much every standard command will write to stdout already, but I have used it often with custom stuff. Here is a contrived example:
$ echo "hello world" | tee >(wc)hello world 1 2 12