Common Linux Shell/SSH Commands

apt (also apt-get, or aptitude)	A command that allows you to install programs, libraries, and such, called “packages” in Linux.
su	A command that allows you to switch to another user (switch user).
sudo	A command that allows you to run another command with administrator privileges.

shell (also console or terminal)	A shell is an interface that allows you to interact with a Linux system. On most graphical systems, you would use a mouse and keyboard to interact with the system, but in a shell, everything is text. In a shell, you use commands you type to interact with and control the system.
SSH	Stands for secure shell. (See shell.)