Final answer:
The term 'otaku' has been popularized by the global fascination with Japanese anime and manga, the proliferation of Internet culture and digital media, and the academic and media discourse surrounding this subculture.
Step-by-step explanation:
The term otaku has been popularized through a combination of cultural forces and sources. Firstly, the global fascination with Japanese popular culture, including anime and manga, has been a significant factor. These forms of entertainment have reached worldwide audiences and have been integral in spreading the 'otaku' concept which originates from Japan. Secondly, the rise of Internet culture and digital media has provided platforms for fans to congregate, share, and popularize niche interests, including those that fall under the otaku umbrella. Lastly, academic and media discourse has contributed to the exploration and spreading of the term, with numerous studies, articles, and discussions analyzing the phenomenon and its global impact. Together, these sources have acted synergistically to bring otaku from a subcultural term in Japan to a widely recognized label used around the globe to describe passionate fans of various aspects of Japanese pop culture.