Key event confusion

What's the difference between "key pressed" and "Key is Down" ?

"Key pressed" only triggers once when you press the key.

"Key is down" is true as long as you hold the key.

edit :yeah wut he said

Difference is when key is not down, but has been pressed.

Its customary to use key is down if you want a constant event.. well constant while its down anyway.

Example: right arrow key is down

object move right

or

up arrow pressed

object jump