How can be used the "^" character at the end of an installation package on apt

Question

I have an special question about APT command-line tool. When I use sudo apt install ubuntu-desktop^ does different things than sudo apt install ubuntu-desktop. I don't know why this happened, and why it do not work with all packages like if you do it with gparted like: sudo apt install gparted^ it does nothing. So I want to know how the final ^ works on apt and why it works just in special cases.