Texture: What do these letters and numbers mean?
The numbers 1 to 4, with subdivisions a, b, and c, are a way to describe how curly hair is:
1 straight, 2 wavy, 3 curly, 4 coily (aka afro textured),
and a to c represent looser to tighter within each category, as shown in the diagram below.
The system was originally created by Andre Walker (Oprah's hair stylist), in the 1990s. If you're interested in Walker and the history of this typing system, it's Wikipedia page has a variety of sources, and a table showing Walker's descriptions for each subdivision.
These terms can be a useful shorthand or starting point for discussing hair texture, but they are not the be-all-end-all. A lot of people have variation in how curly their hair is across their head, for example, I often find tighter curls around the nape of the neck on my clients. Don't worry if you feel like your hair doesn't neatly fit into one description, I'm just using them as a ballpark. If you are unsure whether to describe your hair as curly or wavy: when looking at a single strand of hair, I would describe a curly hair as a three dimensional corkscrew shape, and a wavy hair as a two dimensional S shape. Generally, I don't describe straight hair with this system, as I don't find it a useful way to discuss straight hair (further thoughts).
