PAN: Permanent account number

The PAN structure is as follows: ABCPZ1234C: First five characters are letters, next four numerals, last character letter.

The first three letters are sequence of alphabets from AAA to ZZZ

The fourth character informs about the type of holder of the card. Each holder is uniquely defined as below:
A – Association of Persons (AOP)
B – Body of Individuals (BOI)
C – Company
F – Firm
G – Government
H – HUF (Hindu Undivided Family)
L – Local Authority
J – Artificial Judicial Person
P – Individual
T – AOP (Trust)

The fifth character of the PAN is the first character
(a) of the surname or last name of the person, in the case of a “Personal” PAN card, where the fourth character is “P” or
(b) of the name of the Entity, Trust, society, or organisation in the case of Company/ HUF/ Firm/ AOP/ BOI/ Local Authority/ Artificial Jurdical Person/ Govt, where the fourth character is “C”,”H”,”F”,”A”,”T”,”B”,”L”,”J”,”G”.

The last character is an alphabetic check digit.
source: http://en.wikipedia.org/wiki/Permanent_account_number