In knitting, weaving is a family of techniques used for several purposes in knitting.
The most common use for the technique is when working stranded color patterns, in which two yarns are alternated to certain of the stitches to create patterns. Weaving is used to attach the horizontal strands of yarn that pass unused behind stitches formed with the other yarn to the inside of the fabric. This is usually done to prevent overlong "floats" on the inside to prevent snags and create an even tension in the fabric.
The technique can also be used for decorative purposes if it is done on every stitch, in which case the "inside" of the fabric is used on the outside
Weaving in, or "inlay", is a related but different technique that is used to thread an extra yarn(s) into the fabric without knitting it. The woven yarn(s) need not be the same thickness or color as the knitted yarn, and almost always (but not necessarily) follow the horizontal rows (courses) of knitting. Because the extra yarn simply passes back and forth between the knitted stitches, it can be pulled out unless it is secured in some way at the sides. The resulting fabric is more like a woven texture than a knit because the extra strand reduces its elasticity.