Dual Listing

A company's securities are listed on more than one exchange for the purpose of adding liquidity to the shares and allow investors greater choice in where they can trade their shares.

Investopedia Says:

Dual listing is not a widely used technique though it is thought to improve the spread between the bid and ask prices which helps investors obtain a better price for their security. Hewlett-Packard (HP), for example, is listed on both the NYSE and Nasdaq.

Related Links:
Learn some of the important differences in the way they operate and the securities that trade on them. The Tale Of Two Exchanges: NYSE And Nasdaq

Listing of a security on more than one exchange, thus increasing the competition for bid and offer prices as well as the liquidity of the securities. Furthermore, being listed on an exchange in the East and another in the West would extend the number of hours when the stock can be traded. Securities may not be listed on both the New York and American stock exchanges.