Basically, yes, they're the same. A serger is actually a 5 thread, but the terms are pretty much used interchangably.

I have a serger that is 4 thread. I guess it is termed and overlock. Colleen

The books I have on using a serger seem to indicate that a serger is the machine and overlock is the stitch it forms, regardless of the number of threads. But I have heard the terms serger and overlocker used interchangeably.

Mary

Thank you all very mcuh. That helps me! Enjoy what's left of your week and the coming weekend!

bluejean in ohio

Just beware of the ads for regular sewing machines that claim to serge or do overlock. They do not do the same operation as a serger. There may be an overlock stitch included in the available stitches, but you are not getting a serger when you buy one of these. There will be no cutting blades involved and you will only be using 2 threads instead of 4 or 5.
Carol

No, actually that is NOT correct. A "serger" is technically an overlock machine, that is set up with 3 threads, and lacks the capacity to produce a "safety stitch". The overlock stitch is the "serge", but only if executed with 3 threads. The machine that historically did that operation was the "Merrow" machine (one needle and two loopers). Over time the term "serger" has become more generic, but if you work in the world of machinery "serger" is synonymous with "Merrow", a 3 thread overlock.

"Overlock" is the generic term for the stitch that finishes a raw edge. It describes either a 2 or 3 thread overlock ("serge"); a two thread overlock uses one needle, one looper and a "spreader", only two cones of thread are used.

A machine that not only overlocks the raw edge but also provides a first line of stitching (this is the "safety stitch", one needle and one looper to provide a chain stitch) is designated thusly: "5 thread overlock" or "4 thread overlock". The difference is in how many loopers the configuration provides, and how many cones of thread are required to produce the overlock stitch. A three thread overlock requires one needle and two loopers and is the most secure of the two, requiring 3 cones of thread to complete the stitch; strong enough to join pieces... two thread overlocks are not.