A ticker symbol is an abbreviation used to uniquely identify publicly traded shares of a particular stock or security on whatever market it trades on.
Stocks are usually represented by a combination of letters (typically 3-4), ETFs are generally identified with 3 letters, and mutual funds often have 5-letter combinations that end in the letter “X”, but they can also be alphanumeric. A ticker can consist of a combination of letters, numbers, and sometimes (but not often) both.
A ticker can also refer to a streaming report of stock prices, the most common of which an investor may recognize as the moving line at the bottom of the screen of a financial program.
Here are examples of different characterizations of tickers:
New York Stock Exchange (NYSE) - stocks listed and traded on U.S. exchanges such as the NYSE have symbols with up to three letters
NASDAQ - Nasdaq-listed securities have four-letter symbols