As social media use continues to increase its presence in our lives, so does the language of such platforms. One of the most salient features of social media discourse is the hashtag. Starting its life on Twitter (X) about 15 years ago, the hashtag has seeped from online to offline communication. Yet, it is not clear whether hashtags are words, tags, or something else altogether, nor is it clear what morphological process gives rise to them. This study presents an extensive analysis of 3,423 hashtags from 1,216 English-language tweets, each manually coded for various linguistics features, including position in the tweet, grammatical function, and syntactic integration. Our findings suggest that hashtags are extremely varied and we propose that they are indeed words, arising through a process of hashtagging (which is distinct from compounding). We also argue that some hashtags are syntactically integrated while others constitute parenthetical material.