Complete nonexistence; nothing at all. Used to indicate that something is entirely absent (often in written contexts).
その主張を裏付ける証拠は皆無だ。
There is absolutely no evidence to support that claim.
経験が皆無な人にその仕事を任せるわけにはいかない。
You can't entrust that job to someone with no experience whatsoever.
予算は皆無に近く、計画は中止された。
The budget was nearly nonexistent, so the plan was canceled.