A serger, also known as an overlocker
, is a special industrial-type of sewing machine
that sews with up to 4 threads at a time and also uses a small blade
to cut the edge of a seam
as it sews. Two threads (called the looper
s) loop over the edge of the fabric that the blade has cut, and two needle
s sew them in place with the other two threads. Thus, a serger finishes a seam all in one step. It is a huge time-saver for garment construction, and almost all "professional" garments are constructed using one. Just turn a store-bought
t-shirt inside out and look at the seams, and those are what standard serger seams look like.