KFB is an abbreviation in knitting that stands for "Knit Front Back". It is a popular knitting increase where you knit twice into the same stitch – once through the front of the loop and one more time through the back loop of the same stitch. This technique is used to increase the number of stitches in a row by one. Here are the steps to KFB:

1. Knit one stitch as you normally would.
2. Without slipping the stitch off the left needle, insert the right needle into the back loop of the same stitch from right to left.
3. Wrap the yarn around the right needle counter-clockwise and pull the yarn through.
4. Drop the stitch from the left needle.

After completing these steps, you will have created a little visible purl bar with it. KFB is also known as "Bar Increase" because of this. Sometimes it is also abbreviated as "K1fb" or even "K1f&b".