What is "sideseams"

Usage examples of "sideseams".

You stepped into it, almost as if into a bulky over­coat, and the sideseams wrapped themselves around you, closed their gaskets down, and would not open them again until your purposeful touch reactivated them.

Oblivious to anyone watching, she pulled her petticoats off, and ripped the sideseams of the skirts to the knee.