is a casual variation of the と
particle that is used for quoting something. This use is called 引用（いんよう） in Japanese, which basically translates to ‘reference’, or ‘citation’. って
is almost exclusively used after direct quotations, and will be followed by a verb indicating what type of communication was used. 言（い）った, 思（おも）った, 聞（き）いた, for example.
Mom said, ‘I’ll be back soon’.
The teacher said, ‘That is dangerous’.
Just like with と
, the verb that comes after って
is frequently omitted. This is even more true for って
, as many things are omitted in casual language.
Although often heard, due to って being very casual, it can be considered unnatural to use in sentences that also use the です or ます polite structures. However, if the conversation is formal but friendly (like between a senpai and a kouhai), most people would consider it normal.