Steeking is a shortcut used to knit items like sweaters, in the round, without interruption for openings for sleeves until the end. After completing the section the knitter cuts a straight line along the center of a column of stitches. The "steek" itself is a row of extra stitches where the cut is made. This technique was developed by the knitters of the Shetland archipelago and is mostly associated with Fair Isle patterns.
This probably sounds kind of scary, right? After finishing knitting an intricate pattern, now you are supposed to take scissors to it. Breathe, we're here to help! Before you cut, be sure that your edges are tacked down or sewn to create a nice edge that won't unravel.
So how do you know where to cut? Many knitters will add about 8 stitches or so, to their pattern, knitting in the same colors they've been using. When they are finished, they just carefully cut right down the middle with very sharp scissors. Then they tack the edges flat and pick up the stitches for their sleeve or sew a sleeve in place.
There are three ways you can reinforce your garment for steeking. One option is to sew a couple of columns on either side of the area you want to cut, providing the most protection to unraveling. Using a machine or hand sewing with tread or thin yarn, you can create a secure area to prep your piece for cutting. Sew, then cut, then enjoy!
Another way to prepare the area for steeking is to crochet a column on either side if you're using more "sticky" fibers as non superwash wool. The fibers will act almost like hook and loop tape to keep things secure.
The last way is to just cut blindly and pray for the best. Unreinforced steeking is done using very sticky wool that will mat slightly and felt as you go, to create a secure edge after cutting. Cut slowly and handle the garment carefully. This is surely the most challenging way to steek and should be left to advanced knitters.
Steeking is used for more than just sleeves. With it, you can turn a traditional sweater into a cardigan! Craftsy knitter Ragga Eiríksdóttir shows you how to steek a sweater into a cardigan using a single row of purl stitches. Watch along as she anchors her work using a crochet hook and makes a single crochet ridge all along the purl column on both sides. Then she tackles the scary part... the cutting! Because she has anchored her work, there is little risk for unravelling. So she simply cuts and she's done- just as you will be!
You can learn more about this technique and steeking in general with Ragga's class, The Top Down Icelandic Sweater.