What is American Depositary Receipt?

Legal Definition
An American depositary receipt (ADR, and sometimes spelled depository) is a negotiable security that represents securities of a non-U.S. company that trades in the U.S. financial markets.

Shares of many non-U.S. companies trade on U.S. stock exchanges through ADRs, which are denominated and pay dividends in U.S. dollars and may be traded like regular shares of stock. ADRs are also traded during U.S. trading hours, through U.S. broker-dealers. They simplify investing in foreign securities by having the depositary bank "manage all custody, currency and local taxes issues".

The first ADR was introduced by J.P. Morgan in 1927 for the British retailer Selfridges on the New York Curb Exchange, the American Stock Exchange's precursor.

They are the domestic equivalent of a global depository receipt (GDR). Securities of a foreign company that are represented by an ADR are called American depositary shares (ADSs).
-- Wikipedia