Busty is used to describe woman with a large bosom or chest. A woman's chest area is her bust. A more roundabout term is "well-endowed". Both these are not considered slang or particularly offensive.

Please don't say this to a woman in public, she will feel very offended. Most men talk about women like this amongst themselves.

If you describe a woman as busty, you mean that she has large breasts. (Informal)