keyboard-shortcuts are a combination of a small number of keys, often a single key in combination with
Alt, that results in an action. The action depends on the context in which the keyboard-shortcuts is defined and executed. The action can include operating system tasks, launching of programs, executing menu entries within a program.
Single key keyboard-shortcuts are often called a hotkey or a keymap. Keymaps in the X Windows System environment can be used to define keys otherwise not available on the keyboard and are implemented using its keymap file
~/.XmodMap and the program xmodmap.
For a more expansive description read the Wikipedia article on keyboard shortcuts.