To get along well with someone; to be compatible in personality or tastes (literal origin: 'the horse fits').
新しい隣人とウマが合って、すぐに友達になった。
I got along with the new neighbor and quickly became friends.
初対面なのに馬が合う人もいるから不思議だ。
It's strange how some people click even on first meeting.
仕事のパートナーとはウマが合うかどうかが重要だ。
Whether you get along with your work partner is important.
彼女とは趣味も合って、まさに馬が合う関係だ。
We share hobbies and really hit it off — we're a great match.