means The line where two pieces of fabric or material are joined together, or more broadly any junction or ridge where two things meet.

from From Old English 'seam,' the stitched join of cloth, traceable back to a Proto-Germanic root 'saumaz' — kin to German 'Saum' and related to the idea of sewing itself (the Indo-European root '*syuh-,' to sew or bind). The geological 'seam' of coal or rock, a thin layer pressed between thicker ones, borrows the same image of two masses meeting along a line.