Slip 2, Knit 2, Pass Slipped Stitches Over (S2KP)
The S2KP or slip 2, knit 1, pass slipped stitches over is a basic double decrease that makes the center stitch prominent.
Slip 1, Knit 1, Pass Slipped Stitch Over (SKP)
The SKP, or slip 1, knit 1, pass slipped stitch over, is a pretty common decrease that slants to the left.
Purl 2 Together Through Back Loop (p2tog tbl)
Purling 2 together through the back loop will seem like you're doing it wrong the first couple of times, but if it feels wrong that probably means you're forming this decrease correctly.
Purl 2 Together (p2tog)
Purl 2 together or P2tog is not as common as the knit 2 together decrease, but it is just as simple to make when you need to get rid of a stitch on the purl side of a fabric.
Knit Two Together
Knit two together (k2tog) is a basic and quick way to decrease stitches, which slants slightly to the right. It is the decreasing method that most people learn first.
Slip Slip Knit (SSK)
SSK or slip, slip, knit is an easy way to decrease the number of stitches on your knitting needle. This makes a decrease that leans to the left.
Knit Three Together (k3tog)
Knit 3 together is a right-slanting double decrease that's worked just like a knit 2 together.
Purl Three Together (p3tog)
Use a purl 3 together to decrease two stitches at once on the wrong or purl side of a knitting project.
Slip, Slip, Slip, Knit (sssk)
An sssk or slip, slip, slip, knit, is an easy way to decrease two stitches at a time and have a decrease that leans to the left.
Slip 1, Knit 2 Together, Pass Slipped Stitch Over (sl 1, k2tog, psso)
The slip 1, knit 2 together, pass slipped stitch over decrease begins by slipping a stitch and knitting two together.