The term 'Fellow, informally' can be expressed in two different ways. The first is 'DUDE, ' which is a four-letter word that is often used to refer to a man or boy. It is an informal term of address and is often used to express camaraderie or familiarity. The second is 'MAC, ' which is a three-letter word that is short for 'MACKINTOSH, ' a type of waterproof coat. It is also used as an informal term of address, usually for a man or boy. Both terms are used to refer to someone in a friendly, informal way.