Explanations on Different Airfare Classes (e.g., L, K, Y, etc.)

Have you ever wondered what the different cabin classifications are? Such as L class versus K class? I am flying Delta today (BTW, Delta stands for Don’t Even Leave The Airport) and they are not able to upgrade me because my ticket was issued as a L class. So I decided to look it up:

A - First Class Discounted
B - Coach Class Discounted
Bn- Night Coach Discounted
C - Business Class
Cn- Night Business Coach
D - Business Class Discounted
E - Shuttle Service
F - First Class
Fn- Night Coach in First Class Compartment
H - Coach Class
J - Business Class Premium
K - Coach Class Discounted
Kn- Night Coach Discounted
L - Coach Discounted
M - Coach Discounted
N - Coach Discounted
P - First Class Premium
Q - Coach Discounted
Qn- Night Coach Discounted
R - Supersonic
S - Coach
T - Coach Discounted
U - Shuttle Service
V - Coach Discounted
Vn- Night Coach
W - Coach Premium
Y - Coach
Yn- Night Coach
Z - Business Class Discounted