sk

Skip is not a very common term in knitting since all the stitches are live and will unravel if not worked. Having done some digging, the only thing I can come up with is when picking up stitches along the row side you might have to skip some stitches to ensure the picked up stitches don't pucker or pull. Normally you would pick up and knit 3, skip 1, and repeat. Otherwise, this abbreviation could be a substitute for a slip stitch.

M1A

Make one away is a right leaning single stitch increase. It is the easiest way to make a tidy increase and is perfect for colour work.

To make this increase, take the working yarn and make a loop by twisting it 180 degrees clockwise, place it onto the right hand needle, work the rest of your row/round. When you get to this stitch on the next row/round, work it as normal through the front loop.

k2tog tbl

Knit 2 through the back loop is a single stitch decrease with a twist which gives the stitch a left lean unlike its right leaning k2tog counterpart. It is bulkier and much more visible but easy to make and can be used as a design feature.

ptfl

Purl through front loop is not a term you will encounter often since purling through the front loop is the basic purl stitch.

To make this stitch insert the right hand needle into the working stitch from right to left, the tip of the right hand needle will point left and towards you, wrap the yarn around the right hand needle and pull through the stitch sliding the worked stitch off the left hand needle and leaving the new stitch on the right hand needle.

ktfl

Knit through front loop is not a common abbreviation. This is just another way of saying knit a stitch as normal.

bl

Back loop refers to the back part of the stitch on your needle. Knitting and/or purling stitches through the back loop twists the stitch. This can be used as a design feature.

krl

Knit right loop is a left leaning single stitch increase. It's tidy and easy to make.

Knit up to the stitch you are increasing, with the right hand needle pick up the stitch on the row below inserting the needle from the back to the front, place it on the left hand needle and knit through the front loop.

If you find this increase leaves a hole, knit the lifted stitch through the back loop to twist the stitch and eliminate the gap.

yb

Yarn back means you move the yarn from front of your work (purl position) to back of your work (knit position).

St st

Stockinette stitch is a flat stitch with defined loops. One might say it has the look most people think of when thinking of knitted fabric.

When knitting back and forth you will alternate knit and purl rows. When knitting in the round you will knit every row.

S2KP2

Slip 2 stitches as if to knit 2 together, knit 1, pass 2 slipped stitches over knit stitch. This is a centred double decrease. It is fairly tidy and easy to make.

Insert the right hand needle into two stitches as if to knit, slip them onto the right hand needle (they will be twisted but do not straighten them because they will lay flat when off the needle), knit one stitch, insert the left hand needle into both slipped stitches and bring them over the knit stitch and off the right hand needle.

rev St st

Reverse stockinette stitch is achieved in the same way a regular stockinette stitch is made except the purl (bumpy) size is the right side and the knit (smooth) side is the wrong side.

To make this stitch when knitting back and forth, purl on the right side and knit on the wrong side. To do this in the round, purl every round.

yfon or yfrn

Yarn forward and over needle or yarn over and round needle is used when switching from knit stitch to purl stitch with a yarn over in between.

Bring the yarn to the front, wrap the yarn around the right hand needle with yarn ending up back at the front of work ready to purl.