The phrase "open seam" refers to a break or gap in a seam or stitching, which can cause something to be exposed or come apart.
Sentences with «open seam»
Right sides facing and matching raw edges, stitch the back skirt piece to the main seat piece and trim and press open seam allowance. (idealhome.co.uk)
Open the seams of the shoulder portion of the wrap that is closer to your body than the other shoulder. (abckidsinc.com)
In the picture of the little boy... only the part where it is padded is on the dip in the front below the leg opening seams. (pottytrainingconcepts.com)