The word is not on the dictionary. It's an abbreviation for young persons. That's not a standard word. 맞(: together)+ 팔(:팔로우(follow)'s first character) If you use that word to Korean, some can understand, some can't get it especially most of old man don't understand the word. And some can understand the word but hate to use those abbreviations cause they regard it as a kind of immature act, a rude person.

저는 이해합니다.감사합니다 .

Joo Hyung was kind of right, but it is more natural to translate what they said as: "follow me back". They must have followed you on Instagram, so they are asking you to follow them back as a favor :)

Very strange comment to my photo, thanks

Let's follow each other.