The one-paragraph answer
A serger (called an overlocker outside North America) is a sewing machine that sews a seam, trims the seam allowance with a built-in knife, and wraps the raw edge in thread, all in one pass. It uses loopers instead of a bobbin and runs three to five threads at once. The result is the finished edge you see inside store-bought clothes.
What 2, 3, 4 and 5 thread means
Most home sergers are 3/4-thread. Add a 2-thread option and you get finer edges on light fabric; add a 5th thread and chain stitch and you are into combination machines that also coverstitch.
Differential feed
What a serger cannot do
- Sew a zipper, a buttonhole, or topstitching.
- Sew inside a garment away from an edge: the knife is always on.
- Replace a coverstitch machine for hems (a serger's rolled hem is a different look).
Threading: manual, lay-in, or air
Threading is the thing people hate about sergers. Budget machines use colour-coded lay-in paths and a manual lower looper. Air-threading models push looper thread through a tube with a button. The stitches are the same; you are paying for the minutes saved every colour change.
