What it does
I'm not aware of "Disappear" as an official Magic: The Gathering keyword or ability. It's possible you're thinking of a different mechanic with a similar feel.
You might mean Vanishing, a keyword from Time Spiral block. A permanent with Vanishing enters with a number of time counters, loses one on your upkeep, and gets sacrificed when the last one is removed. Unlike Phasing or Suspend, the permanent is gone permanently once counters run out—you can't "blink" it back without other support.
Alternatively, you could be referencing Phasing (permanents "phase out" and temporarily leave, then return), or a card-specific effect. If you can confirm the exact card or wording you saw, I'll give you the precise rules breakdown and how it plays in Commander.
