Elias Howe (1819–67) invented the lockstitch sewing machine; in 1851 Isaac M. Singer (1811–75) invented the first practical domestic sewing machine.    From Wordnik.com.  [c. Machines and Industrial Techniques] Reference

The lockstitch uses two threads, an upper and a lower.    From Wordnik.com.  [words are not enough] Reference

In short, the chainstitch is a crochet or knitting stitch, while the lockstitch is a weaving stitch.    From Wordnik.com.  [The Age of Invention : a chronicle of mechanical conquest] Reference

The two threads of the lockstitch cross in the materials joined together, and the lines of stitches show the same on both sides.    From Wordnik.com.  [The Age of Invention : a chronicle of mechanical conquest] Reference

The term "single needle stitching", often found on dress shirt labels, refers to lockstitch, as opposed to chain stitch which unravels easily and is usually used on lower quality garments.    From Wordnik.com.  [words are not enough] Reference

Howe, the American inventor, secured a patent for an improvement in sewing-machines, which embodied the main features of the machine used at present; to wit, a grooved needle provided with an eye near its point, a shuttle operating on the side of the cloth opposite the needle to form a lockstitch, and an automatic feed.    From Wordnik.com.  [A History of the Nineteenth Century, Year by Year Volume Two (of Three)] Reference

Then the take-up arm pulls the excess upper thread (from the bobbin area) back to the top forming the lockstitch ideally in the center of the thickness of the material, the tension mechanism prevents the thread from being pulled from the spool side, the needle is pulled out of the cloth, and the feed dogs pull the cloth back one stitch length, the cycle is repeated as the machine turns mechanically.    From Wordnik.com.  [words are not enough] Reference