expression, ichidan verb
make eye contact
Used when two people look into each other's eyes, often intentionally or in a significant moment.
彼と目を合わせることができなかった。
I couldn't make eye contact with him.
話すときは相手と目を合わせましょう。
Let's make eye contact with the other person when speaking.
目が合う is intransitive, meaning 'eyes meet' (happens spontaneously), while 目を合わせる is transitive, meaning 'to make eye contact' (intentional action).
Compound of 目 (eye) + を (object marker) + 合わせる (to put together, to match). Literally 'to match eyes'.