noun
Refers to the line or gap where two parts meet, such as in sewing, woodworking, or construction.
この合わせ目がきれいに仕上がっている。
This seam is finished neatly.
板の合わせ目に隙間ができた。
A gap appeared at the joint of the boards.
継ぎ目 also means a joint or seam, but often implies a connection or splice, while 合わせ目 emphasizes the meeting line of two surfaces.
Compound of 合わせ (awase, 'joining') + 目 (me, 'eye; point; line'). The exact historical derivation is straightforward.