Knitting socks is a lot of fun, but knitters throw around a lot of terms related to knit socks and that parts of a sock that you might not understand if you've never knit a sock before.
Here's a rundown, from the top down, though of course socks can also be worked from the bottom up.
The sock cuff is the top part of the sock, which is usually worked in some kind of ribbed stitch to help the sock cling to the leg.
In socks that have decorative legs, the pattern stitch used on the leg can be used throughout, so that there isn't really a cuff.
Likewise socks can have ribbing all the way down the leg. Here the cuff is show in pink.
Moving down the leg you find the part of the sock that is known as the leg. This part of the sock may have a different stitch pattern from the cuff.
Here the leg is worked in Stockinette Stitch in red yarn.
Not all socks use a heel flap construction (some use a short row heel, or a different construction), but many do, and if you're knitting from the top down, this is the part of the sock you will come to next.
The heel flap is typically worked back and forth in rows on about half of the stitches of the sock.
Heel flaps are commonly worked in a simple repeating slip stitch pattern, and the first stitch of each row is usually slipped for ease of picking up stitches later on. Heel flaps can also be decorative, for instance, worked in two-colors on a sock with colorwork, or even with cables or other stitch patterns worked on them.
The heel flap in the sample sock shown is worked in dark blue.
Once the flap has been worked, a section of short rows shapes the cup of the heel. This is the turn that makes it possible to knit an L-shaped sock rather than a tube.
It's also the part that scares new sock knitters the most, but the important thing is just to pay attention to what the pattern is asking you to do and do what it says; don't question it.
There's a pretty standard formula for working a heel turn, too. You usually start by slipping the first stitch, working across half the heel stitches plus one, work a decrease and a wrap and turn to prevent a hole in the heel.
Slip the first stitch, then purl across a few of those stitches you just worked (it's often 5), work another decrease and another wrap and turn.
Each row you will work one more stitch before you turn until you've worked all the stitches.
The heel turn is shown in light blue.
Once the heel turn has been worked, you pick up stitches along the sides of the heel flap in order to join the leg stitches back into the work and resume knitting in the round.
You have more stitches now than you did when you were knitting the leg. To get rid of them, you'll work regular decreases along the sides of the foot. This wedge-shaped area is known as the gusset. The top of the foot, which is worked at the same time, is known as the instep.
Pattern stitches from the leg are often continued on the instep, but not always. In the sample sock the gusset and instep are worked in purple.
Once you have worked back down to the same number of stitches you had in the leg (typically), you will work straight for some time to knit most of the remaining length of the foot.
The foot here is worked in yellow.
One more bit of shaping gets us to the end of the sock. The sock toe usually involves four decreases in a round, which is worked every other round until about half of the stitches have been decreased, then every round until just a handful of stitches remain.
The toe of this sock is worked in green.
The last stitches can be finished off simply by threading the yarn through and closing the toe, like you would for the top of a hat, or you can sew them together using Kitchener Stitch.