반말(informal speech), occasionally called 해채, is a form of Korean Language used among peers or to people who are younger than you. 반말 isn't commonly used for first meetings; usually friends ask permission to use 반말 after getting to know each other. Towards younger classmates(후배) and children 반말 is common and acceptable to use without asking permission. It should be noted that the use 반말 towards a person senior to you in age or rank without permission is considered disrespectful.
Most 반말 and their 존댓말(formal speech) counterparts usually only differ by the use of '요' at the end of the sentence. However, some 반말 has a slight structure difference from its 존댓말 form.
|잘 지냈어요?||잘 지내?||How have you been?|
|김치를 먹고 싶어요.||김치를 먹고 싶어.||I want to eat Kimchi.|
|모르겠어요.||몰라.||I don't know.|
|수업 끝나면 전화해요.||수업 끝나면 전화해.||Call me when the class finishes.|