What is a Chord?
A chord is a set of keys of the computer keyboard that are pressed together, e.g. Ctrl+C, or Ctrl+Shift+Tab.
A chord typically contains a modifier key such as Ctrl, Shift, Alt, or WinKey that doesn't do anything when pressed, which means you can safely press and hold the modifier key, then press the other key of the chord that would normally do something when pressed alone, e.g. the "C" key would normally type the letter "c" if you press it alone, but when used in a chord, it can activate a keyboard shortcut instead.
Note: the WinKey is rather unique because it does do something when released (it opens the start menu), but doesn't do anything when pressed. If you press and hold it and activate a keyboard shortcut, such as WinKey+D, the default behavior of the WinKey is cancelled and the start menu won't open.
What is the Difference Between Chord and Keyboard Shortcut?
A keyboard shortcut is often a chord that includes a modifier key, such as the Ctrl key (for application-level keyboard shortcuts) or the Alt key or WinKey (for operating system-level keyboard shortcuts), however, not all keyboard shortcuts are chords.
For example, the F2 key is often a keyboard shortcut (or "hotkey") to rename the currently selected item. In this case, the key is pressed alone, which means that it isn't a chord.
On the other hand, not all chords are necessarily keyboard shortcuts. To form a chord, all you need to do is press multiple keys together.