(fa'net'ik' al'fa'bet) n.

1. in linguistics it refers to a standardized set of symbols used in phonetic transcription.
2. any of various systems of code words for identifying letters in voice communication.

i.e. used often in telephons conversations to clearly identify: part numbers, strings of computer language code, Email addresses, etc. so as to not confuse similiar sounding letters or homonyms.

ex.: "... my Email address is IanC@123.com..."
ex. con't: could be misundertood as: ENC@123.com
ex. still con't: so to clarify, one could say: "... that's India Alpha November Charlie, at; numbers one, two, three, dot, Charlie Oscar Mike..."

There are numerous variations of Phonetic Alphabets. The official versions include:
English, American (ex-military), International, International (ex-aero), NATO & International Aviation, American (police), Italian and German.

Most comonly used is the NATO & International Aviation tabled here:

A - Alpha
B - Beta or Bravo
C - Charlie
D - Delta
E - Echo
F - Foxtrot
G - Golf
H - Hotel
I - India
J - Juliet
K - Kilo
L - Lima
M - Mike
N - November
O - Oscar
P - Papa
Q - Quebec
R - Romeo
S - Sierra
T - Tango
U - Uniform
V - Victor
W - Whisky
X - X-ray
Y - Yankee
Z - Zulu