Informal communication takes place in intimate circles, usually among friends and family, and formal communication takes place among people whose relationship is formal. In informal writing and speaking, we use lot of contractions such as I'm, you're; I've, I'd etc. Idiomatic expressions or phrasal verbs, exclamation, repetition, tag questions and use of slangs etc, are features of informal writing and speaking. The following letter is an example of an informal letter.