"Wassup" is an informal greeting used among friends and peers. It is a contraction of the phrase "What's up?" and is typically used to ask how someone is doing or what is happening in their life. The tone is casual and friendly.
The word "wassup" originated in African American Vernacular English (AAVE) and gained popularity in the 1990s, especially with the rise of media that portrayed casual, friendly interactions among young people. It has since entered mainstream usage, particularly in informal contexts.