In dictionaries and grammar notes, conj. is the short written form of conjunction — a joining word that hooks parts of a sentence together, such as and, but, or, because, and although. You almost never say “conj” out loud; it lives on the page, where there is no room for the full word. Though actually, conjunction has other meanings in English too (planets lining up, for example), but this abbreviation is only the grammar label. If a dictionary marks a word conj., it is telling you how that word works in a sentence, not what it means.

連接詞（書面縮寫；台灣說「連接詞」，大陸常說「連詞」）