In the digital age, the widespread usage of slang in online fan communities has evolved into a linguistic phenomenon reflecting member identity, creativity, and solidarity. This research aimed to analyze the types and the functions of slang words used by the NCTZENBASE Community in X. This research used a qualitative research method by applying a case study design. This research used document analysis and employed Allan & Burridge's (2006) theory. The result showed that there were 98 data taken from posts and comments in the NCTZENBASE Community. In this research, the researcher grouped the data into single, duplet, triplet, quadruplet, and quintuplet. Based on findings, duplet grouping of types of slang is the most found in the NCTZENBASE Community, there are total of 35 data (35.71%), single has 29 (29.59%), triplet has 15 (15.30%), quadruplet has 17 (17.34%), and quintuplet has 2 (2.04%). Furthermore, Duplet grouping of functions of slang is the most found in the NCTZENBASE Community, there are total of 32 data (32.65%), single has 30 (30.61%), triplet has 27 (27.55%), quadruplet has 6 (6.12%), and quintuplet has 3 (3.07%). Based on overall results, the most widely used type of slang by the NCTZENBASE Community is the fresh and creative type which is shown by a total of 78 data, or 34.97%, due to die-hard fans like NCTzen, they are heavily influenced by the need to creatively express group identity while establishing direct connections with fellow members and their idols. Additionally, the most frequently appearing and dominant function is to address function with 87 data (39.01%), since communication in this community is interactive and personal, both among members and between fans and idols, utilising slang as an address becomes a crucial aspect of developing a sense of closeness, solidarity, and active engagement in communal conversations.