Seam is a noun: the line where fabric is stitched together, or a thin layer of coal or other mineral in rock. Seem is a verb meaning to appear or give the impression of something. Remember: a seam is sewn, but things seem to be a certain way.
The core difference
Seam is a joined line or layer, while seem means to appear to be.
- seam — a stitched join, or a thin layer of mineral in rock: The seam on her sleeve had come undone.
- seem — to appear or give the impression: She seems happy with her new job.
How to tell them apart
Seem has a double e, like the two eyes you use when something seems a certain way to you. Seam is a physical thing you can see and touch, such as a stitched join or a layer of coal.
The mix-up usually appears in phrases such as it seams like, which should be it seems like. Bursting at the seams is the one common idiom that correctly uses seam.