I see 部 with nouns in hashtags on Instagram (like #ねこ部), but I can only find dictionary definitions online. I'm also unsure of the correct reading of the kanji, so any help would be appreciated.
I am not familiar with hashtags trends and what not, but it might mean they are cat lovers.
部 is usually read as ぶ and usually means department, group, division, club. Although usually used in company jargon, this time it seems to be used to indicate that that person is in the cat group/club... maybe