The Fia info was copied from this site. The info in purple was added by me.
Fia's Hairtyping System
FIRST CLASSIFIER:
The straight ones
1a - stick straight
1b - straight but with a slight body wave, just enough to add some volume, doesn't look wavy
1c - straight with body wave and one or two visible S-waves (e.g. nape of neck or temples)
The wavy ones
2a - loose, stretched out S-waves throughout the hair
Beachy waves, Rock star waves
2b - shorter, more distinct S-waves (similar to waves from braiding damp hair)
Princess hair.
2c - distinct S-waves and the odd spiral curl forming here and there
Mix of waves, curls, and some pieces that have mixes of S and C shapes.
On naturallycurly.com it is often called "wurly" hair.
The curly ones
3a - big, loose spiral curls
Like a telephone cord (anyone else old enough to know what that is)
3b - bouncy ringlets
Ringlets the size of a pinky finger.
3c - tight corkscrews
Ringlets the size of a pencil or straw
The really curly ones
Common among African Americans.
4a - tightly coiled S-curls
4b - tightly coiled hair bending in sharp angles (Z-pattern)
SECOND CLASSIFIER
What (most of) your individual strands look like
F - FineThin strands that sometimes are almost translucent when
held up to the light. Shed strands can be hard to see even against a
contrasting background. Similar to hair found on many people of
Scandinavian descent.
You can also try rolling a strand between your thumb and index finger.
Fine hair is difficult to feel or itfeels like an ultra-fine strand of
silk
M - MediumStrands are neither fine nor coarse. Similar to hair found on many Caucasians.
You can also try rolling a strand between your thumb and index finger.
Medium hair feels like a cotton thread. You can feel it, but it isn't
stiff or rough. It is neither fine or coarse.
C - Coarse
Thick strands that where shed strands usually are easily identified
against most backgrounds. Similar to hair found on many people of Asian
or native American descent.
You can also try rolling a strand between your thumb and index finger.
Coarse hair feels hard and wiry. As you roll it back and forth, you may
actually hear it.
THIRD CLASSIFIER
Your overall volume of hair
Put your hair in a ponytail with as much hair as possible in it. Don't
bother with the way it looks - the goal is to have most/all of your hair
in there. If it means it sits smack dab on top of your head, put it
there.
Measure the circumference of the ponytail. If you have bangs and/or you
can't get all of your hair in there adjust according to how much of your
hair you have measured.
To measure the circumference - take a piece of string, or a soft tape
measure (the kind used by dressmakers). Wrap the string or tape measure
around
your ponytail - just below the elastic you have in to hold the ponytail
together. Read the corresponding number from the tape measure, or hold
the string at the length you've measured and use a ruler to determine
how much it is. The number given is the circumference of your ponytail.
i - thin (less than 2 inches/5 centimeters)
ii - normal (between 2-4 inches or 5-10 centimeters)
iii - thick (more than 4 inches/10 centimeters)
Naturally Curly
link with pictures of curl patterns.
Your curl pattern (or lack of curl pattern) may not fit neatly into one category. It is common to see a mix of curl patterns on one head. Some hair just simply doesn't fit any description.
Figuring out hair texture can be tricky as well. Your hair stylist should be able to tell you what your texture is. If you compare hair with friends, this should help you to figure out your texture. Livecurlylivefree.com has a service where you can send in your hair and they will tell you elasticity, porosity, and texture.
My hair is 2bFi.
On a good day I'm 2cFi.
What does all of this mean? The link explains it.