"Seam peaking" is a term used to describe seams that have popped up a bit and are more visible than usual. Seam peaking can be a frustrating carpet installation problem for both the installer and the consumer. Although seams in carpet are necessary and common, many consumers expect them to be invisible, which in reality cannot be guaranteed. We take extra precautions, like using good seam tape, special carpet irons and attention to seam layout, to avoid peaking seams during your installation.
See the bulletin from the Carpet and Rug Institute for a detailed description (Seam Peaking information )
Pelletier Rug has a nice video to demonstrate the issues around seam peaking Pelletierrug.com Link