Colloquial contraction of という, used to explain what something is called, what it means, or to quote speech/thought. Very common in casual conversation.
See also: という
「エコ」って言う言葉をよく聞く。
I often hear the word called "eco."
田中さんっていう人から電話があったよ。
There was a call from someone called Tanaka.
Tanaka said he can't come today.
彼は来ないっていう話だよ。
The story is that he's not coming.
I have a dog named Sakura.
What 'eco' means is being environmentally friendly.
What do you call this in Japanese?