Investopedia explains Ticker Symbol
Stock symbols are the most recognized type of ticker symbol. Stocks listed and traded on U.S. exchanges such as the NYSE have symbols with up to three letters. Nasdaq-listed stocks have four-letter symbols.
Ticker symbols for options are structured to represent the underlying stock ticker they are based on and also their expiration date and contract type (either a put or a call option). Mutual fund ticker symbols are usually alphanumeric and end with the letter X to differentiate them from stock symbols.
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