expression
Colloquial contraction of というのは, used to define or explain a term or topic. Common in casual speech.
See also: って
「ありがとう」ってのは、感謝の気持ちを伝える言葉だ。
"Arigatou" means a word to express gratitude.
彼が言った「すぐやる」ってのは、本当にすぐやるってことじゃないんだよ。
When he says "I'll do it right away," it doesn't mean he'll actually do it right away.