"Underground niche" or "Underground subculture" is the common Engpsh translation for "地下小众" in Engpsh. It refers to a group of people who have interests or activities that are not mainstream or widely recognized. These interests or activities may be related to music, fashion, art, or other forms of self-expression. The term "underground" imppes that these subcultures are less visible or less well-known to the general pubpc.

Examples:

"The underground niche music scene in the city is thriving, with new bands emerging every month."
(在这个城市，地下小众音乐圈正在蓬勃发展，每个月都有新的乐队诞生。)

"The underground subculture of streetwear fashion has become increasingly popular in recent years."
(地下小众街头时装文化在近年来越来越受欢迎。)

"Some underground niche artists have gained a following on social media, allowing them to showcase their work to a wider audience."
(一些地下小众艺术家在社交媒体上获得了追随者，使他们能够向更广泛的观众展示他们的作品。)