Granny Square
a motif built from double crochet clusters and chain spaces, worked in rounds and joined into larger pieces

The granny square isn't a single stitch, it's a motif: a small square built from double crochet worked in groups of three (clusters), separated by chain spaces, worked outward in rounds from a center ring. Because it has no single abbreviation, most patterns spell out "granny square" or give it its own diagram.
Each round adds a ring of clusters around the outside of the last one, with chain spaces at the corners that let the square grow while staying flat. Squares are typically worked separately, then joined edge to edge into blankets, bags, or garment panels.
How to work it
- Make a slip ring or chain 4 and join with a slip stitch to form a ring.
- Round 1: chain 3 (counts as first double crochet), work 2 more double crochet into the ring, chain 2, then repeat [3 double crochet, chain 2] three more times into the ring. Join with a slip stitch to the top of the starting chain 3. You now have 4 clusters and 4 corner spaces.
- Round 2: slip stitch into the next chain-2 corner space. Chain 3, work 2 double crochet, chain 2, 3 double crochet into that same corner space (this is one corner). Chain 1, then work 3 double crochet into the next corner space to start the next corner. Repeat around, joining at the end of the round.
- Continue adding rounds the same way, working a full corner (3 dc, ch 2, 3 dc) into each corner space and a plain cluster (3 dc) into the chain-1 spaces along each side, until the square reaches the size you want.
When to use it
Granny squares are worked flat in rounds, so they're forgiving of tension changes between sessions, easy to pick up and put down, and simple to join into anything from a single potholder to a full blanket. They're a common first "pattern" after learning chain, single crochet, and double crochet, since the whole motif is built from stitches you already know.