Formal language is a style of English used in certain situations, such as official notices and letters. It has features that make it different from the type of English we use in everyday situations.
We will let you know if you are a winner. (everyday (informal) English)
Successful contestants will be notified. (formal English)
Official language uses more formal vocabulary than everyday language.
winner (everyday English)
successful contestant (formal)
let you know (everyday English)
notified (formal English)