Slang is a non-standard language or a language that is used unofficially. The purpose of this research is to discover the types and functions of English slang words used by Generation Z on WhatsApp. The data sources were WhatsApp conversations taken by college-aged teenagers on a daily basis. This is a qualitative study, with the researcher's primary focus in data collection being content analysis. In this study, the researcher discovered 50 slang terms based on Allan and Burridge's (2006) theory and then classify that slang into seven functions, which are as follows; Starting a relaxed conversation (27 occurrences), expressing an impression (12 occurrences), creating an intimate atmosphere (5 occurrences), addressing (3 occurrences), abusing people (3 occurrences), humiliating (0 occurrences), and expressing intimacy (0 occurrences) and five types, namely, Fresh and creative (7 occurrences), flippant (9 occurrences), imitative (12 occurrences), acronym (14 occurrences), and clipping (8 occurrences). As a result, Generation Z appears to have used this slang to increase the intimacy of their daily WhatsApp conversations.