How to close a program that has frozen.

Options:

1. Close all programs related to that program (including multiple windows of the program)

Use the KillAll feature to kill a program.
Press Alt+F2 and type in gnome-terminal to open a terminal session.
Inside of the terminal type in sudo killall <application-name>.


2. Close a program with your mouse cursor.

Use the xkill feature to kill a program you click on

Press Alt+F2 and type in gnome-terminal to open a terminal session.

Inside of the terminal type in  xkill; then click on any window to kill it.