What is a letter writing

An exchange of communication between the sender and the receiver.

Explanation:

Whether formal, informal or semiformal, letter writing entails an exchange of communication between two parties.

For formal letters, two addresses are included. Language is also formal. Can be written to organizations, institutions, etc.

Informal and semiformal letters on the other hand are letters written to people we know. The language can be less formal. It includes letters to one's dad, mum, friend, etc.

Semiformal letter can be written to the principal of one's high school.