BO and CO mean “bind off” and “cast on“, respectively.

k means a knit stitch and p means a purl stitch

kfb or pfb means “knit or purl into the front and back of a stitch”

Decreases:

K2tog (“knit two together”) — Work to the two stitches to be decreased, insert the right-hand needle into the first two stitches as if to knit, wrap yarn around needle in normal manner, slip the two stitches off together and drop them. This creates a right-leaning decrease.

SSK (“slip, slip, knit”) — Work to the two stitches to be decreased, slip two stitches one at a time to the right-hand needle, as if to knit; insert the left-hand needle into the two stitches from front to back, knit the two stitches together and drop them. This creates a left-leaning decrease.

S1, K1, PSSO (“slip one, knit one, pass slipped stitch over”) — This results in a similar look to the SSK but can appear less tidy. Work to the two stitches to be decreased, slip next stitch to the right-hand needle as if to knit, knit next stitch, pass slipped stitch over knit stitch. Also creates a left-leaning decrease.

Increase:

Yarn-over increase (YO) or “eyelet increase” — The simplest increase is to do a yarn-over between two existing stitches. On subsequent rows, the yarn-over will be knitted, making a new stitch. This disadvantage of this method is that a small hole (eyelet) is produced at the yarn-over. This can be improved by twisting the yarn-over stitch – similar to a “make one” (below).

Raised Increase (M1L)– Lift the strand connecting two knitted stitches in the row below onto the left needle (effectively producing a yarn-over) and knit it, either normally or twisted. This method (especially if twisted) leaves almost no hole, since forming the yarn-over stitch from the (presumably tight) connecting strand draws the two neighboring stitches together.

Bar increase (KFB)– Knit the stitch normally but without transferring the knitted stitch to the right needle; the same stitch is then knitted through the back loop. (Knitting through the front loop again is not feasible, since it would undo the first stitch.) This increase makes a bar or a nub on the fabric.

Moss increase — Knit the stitch normally but without transferring the knitted stitch to the right needle; the same stitch is then purled. This increase makes a bar or nub on the fabric.

Lifted Increase — For a right-side increase, knit into the right leg of the stitch of the row below the next stitch to be knit, then knit the next stitch. For a left-side increase, knit one stitch, then knit into the left leg of the stitch of the row below it. This kind of increase can be visually subtle.

“Make One” (M1) — Place a half-hitch loop on the needle between two stitches, either before or after, and twisted either left or right, depending on desired effect.

Column of Increases — A second strand of yarn or roving is passed up the piece. The second strand is used to make an extra stitch in each row by knitting a doubled stitch up from the lower row. The resulting piece has one more stitch in each row and each row is in the shape of an inverted V. The column of increases is used to make square sweater yokes.