Psionic focus is a mental state unique to psionic creatures. Many psionic abilities and feats work either by maintaining or expending psionic focus.
Meditating to gain psionic focus is a full-round action that provokes attacks of opportunity. Once you are psionically focused, you remain focused until you expend your focus, become unconscious, or go to sleep (or enter a trance, in cases such as elves).
You may still gain psionic focus even if you have depleted all of your power points.