What is a Ticker symbol?

Answer 1

Both previous answers are correct.
A few cheats:

Any symbol with 3 or fewer letters is listed on an exchange (IBM, GE, M - Macys, COF - Capital One, etc.).

4 letters generally means it trades on the NASDAQ (DELL, MSFT - microsoft, SHLD - Sears Holdings, GOOG - google, etc.)

5 or more letters means it is either a pink sheet stock, which was delisted because it did not meet certain financial criteria to stay listed, or that it is an overseas stock, tecnically an ADR or american depository receipt. Pink sheet stocks are loosely regulated and are often trade at low prices and referred to as penny stocks. International stocks might be perfectly fine.

Answer 2

The 1 to 4 letter symbol used to get trading price quotes on companies on the stock exchange .
(Instead of the long winded total name)
For example
IBM = International Business Machines
GE = General Electric
BPT = Prudhoe Bay Trust
C = Citibank ( Citigroup Inc )

Answer 3

A ticker symbol is used to identify publicly-traded shares of a corporation on a particular stock market.

Go here for a better explanation...http://en.wikipedia.org/wiki/Ticker_symbol