what are formal and informal letters?
Formal letters: These letters include applications, letters to editors, official letters, letters to and from organizations, government departments etc. These letters have an objective or business-like style of writing.
Informal letters: These letters include letters to parents, relatives, friends etc. These letters have an easy and conversational language.
While writing formal letters, one should ensure that it is not too extensive. These letters are supposed to be short and to-the-point.