expression, i-adjective
considerable; formidable; tremendous; really something else
Casual expression meaning something is not half-hearted; it's impressive, extreme, or exceptional. Often used in spoken Japanese.
See also: 半端ない
あの新人の実力は半端じゃない。
That new guy's ability is really something else.
今日の暑さはハンパ
This heat today is no joke, huh.
More contracted and slangy form of 半端じゃない, with the same meaning.
From 半端 (half-hearted, incomplete) + negative じゃない, literally 'not half-hearted', used idiomatically to mean 'not ordinary' or 'impressive'.