Joss Stone is 2A Sandra Oh is 2B

Type 2: Wavy hair
Type 2 hair falls into the great divide between Type 1, straight hair, and Type 3, curly hair. A relatively unusual type, wavy hair tends to be coarse, with a definite "S" pattern to it. By that I mean the wave forms throughout the hair in the shape of the letter "S". Your hair is wavy, or Type 2, if it curves in the "S" shape while laying flat against the scalp, instead of standing away from the head the way curly hair does. Supermodel Yasmeen Ghauri, actress/model Isabella Rosellini and actress Jennifer Aniston of Friends (the one who sparked a craze for the ubiquitous "Friends haircut" of the mid-1990s) are all Type 2s. Type 2s are often confused with Type 3s because it is easy to get curly hair to lay flat and look wavy. But don't be fooled: you can't get Type 2 hair to look like Type 3 without a lot of work. Why? The hallmark of wavy hair is that it sticks close to the head: even if you cut it in layers, it won't bounce up. There are three Type 2 subtypes: A, fine and thin; B, medium-textured; and C, thick and coarse. Type 2A is very easy to handle, easily  blowing out into a straighter style or taking on curlier looks with relative ease. Types 2B and 2C are a little more resistant to styling and have a tendency to frizz

Nicole Kidman is 3A Juliana Margulies is 3B Rachel True is 3C

Type 3: Curly hair
With curly hair, there is a definite loopy "S" pattern. Pluck out a hair, stretch it out. Notice the curvy lines. Looks like s stretched-out Slinky, doesn't it? Most people think curly hair is coarse, but actually it is usually baby soft and very fine in texture – there's just a lot of it. Because the cuticle layers don't like as flat, curly hair isn't as shiny as straight or wavy hair. The hair doesn't have a very smooth surface, so light doesn't reflect off of it as much. When curly hair is wet, is usually straightens out. As it dries, it absorbs the water and contracts to its curliest state. Those of you with Type 3 hair know all too well that humidity makes curly hair even curlier, or even frizzier.

If you're a Type 3, your hair has a lot of body and is easily styled in its natural state, or it can be easily straightened with a blow-dryer into a smoother style. Healthy Type 3 hair is shiny, with soft, smooth curls and strong elasticity. The curls are well-defined and springy: pull out a strand of hair and stretch it; it won't snap in two. Damaged Type 3 hair is usually frizzy, dull, hard and dry to the touch, with fuzzy, ill-defined curls.

There are three subtypes of curly hair. Type 3A, hair that is very loosely curled like Julia Robert's or Susan Sarandon's is usually very shiny with big curls. The shorter the hair, the straighter it gets. The longer the hair the more defined the curl.

Type 3B, on the other hand, is hair with a medium amount of curl, ranging from bouncy ringlets – think of Shirley Temple – to tight corkscrews – think of actress Cree Summer of television's Sweet Justice of jazz singer Cleo Laine. It's not unusual to find both subtypes coexisting on the same head. In fact, curly hair usually consists of a combination of textures, with the crown being the curliest part.

Type 3C, is hair with tight curls in corkscrews. The curls can be either kinky, or very tightly curled, with lots and lots of strands densely packed together. Some people refer to this as "big hair." Getting this type of hair to blow-dry straight is more challenging than for 3A or 3B, but it usually can be done. This includes those with very tight curls but finer hair, as well as coarser hair. 3C has really really tight curls, like pencil or straw circumference. 3B is like sidewalk chalk or salt shaker circumference, and 4A is like coffee stirrer circumference.

Nadia Turner is 4A Erykah Badu is 4B.

Type 4: Kinky hair
If your hair falls into the Type 4 category, then it is kinky, or very tightly curled. Generally, Type 4 hair is very wiry, very tightly coiled and very, very fragile. Like Type 3 hair, Type 4 hair appears to be coarse, but it is actually quite fine, with lots and lots of this strands densely packed together. Healthy Type 4 hair won't shine, but it will have sheen. It will be soft to the touch and will pass the strand test with ease. It will feel more silky than it will look shiny. Oprah, Whoopi Goldberg and the actress Angela Bassett are all Type 4s.

Type 4 hairs looks tough and durable, but looks can be deceiving. If you have Type 4 hair, you already know that it is the most fragile hair around. Why? Type 4 hair has fewer cuticle layers than any other hair type, which means that it has less natural protection from the damage you inflict by combing, brushing, curling, blow-drying and straightening it. The more cuticle layers in a single strand of hair, the more protection it has from damage. Each time you damage your hair – fire up the curling iron, fry it with chemicals – you break down a cuticle layer, robbing your hair of much-needed moisture. I cannot emphasize this enough. It's like taking a wire and bending it again and again. Eventually, it's going to snap and break.

Many women with Type 4 hair rely on chemical relaxers to make hair easier to control. In its natural states, sometimes Type 4 hair doesn't grow very long because every time you comb it, it breaks. (Of course, if you have dreadlocks and never comb them or keep them braided, your hair can and does grow quite long.)

There are two subtypes of Type 4 hair: Type 4A, tightly coiled hair that, when stretched, has an "S" pattern, much like curly hair; and Type 4B, which has a "Z" pattern, less of a defined curl pattern (instead of curling or coiling, the hair bends in sharp angles like the letter "Z"). Type 4A tends to have more moisture than Type 4B, which will have a wiry texture. But what if your hair has been chemically straightened? How can you tell which subtype you belong to if your hair is relaxed? You'll need at least one inch of new growth to tell. Pull at the roots. If you can see a definite curl pattern, then it's an A, if not, then it's a B.

Addendum: 
Type 4 hair can range from fine/thin to wiry/coarse strand texture.  Generally, this hair is densely packed to give the appearance of very thick but fragile hair.  4A hair has a clearly visible curl and wave pattern that ranges from pen size curls to pen spring size coils.  4B hair has a tighter wave pattern and kinks of various size.  This texture does not exhibit the shine or silkiness of looser type curls, but instead has sheen, and a soft, almost cotton-like feel. As with other types of curly hair, showing the true length can be an extra challenge, as the hair may grow “up” or “out” before starting to hang down. In its unlocked/unbraided state, type 4 hair is known to shrink up to 75% of the actual hair length.  With the proper care and technique, type 4 hair is indeed resilient, manageable, durable, growable and easy to control.