Formal and informal letter difference.

1) A letter is said to be formal when it is written for official or professional communication. 2) They are written for business.

1) A letter is said to be informal when it is written in a friendly manner to someone. 2) They are written to friends and relatives for personal communication.

Explanation:

Formal letters are written for official or any other people who you are related to business.

Informal letters are written for personal things who you are related to your familiar.

Formal letters are official and more business like but informal can be to friends and family