An American Depositary Receipt (or ADR, for short) is a way in which US investors can trade shares of non-US companies without using their local exchanges.
Because they are issued by US financial institutions and traded on US exchanges, many of the complications associated with buying shares abroad are negated with ADRs, Dividends and profits from share price movements will all be paid in US dollars.
For a non-US company, ADRs are a good way to raise capital and gain more exposure to US equities investors.