Informal

[Sonia]

Not in the regular, usual, or established form; not
according to official, conventional, prescribed, or customary forms or
rules; irregular; hence, without ceremony; as, an informal writting,
proceeding, or visit.

[Greta]

Having a relaxed, friendly, or unofficial style, manner, or nature.

[Oralee]

A more [proper] [way to say] slang.

[Michiko]

not formal or official: