I'll make this really quick and simple:
The absolute max is the highest point.
The absolute min is the lowest point.
Check it out:
f has an absolute max of 2 at x = 2.
(This is also a relative max!)
f has an absolute min of -2 at x = -3.
(This cannot be a relative min, since it doesn't
have points on BOTH sides to compare it to.)
|Endpoints cannot be relative extrema!|
|Endpoints CAN be absolute extrema!|