The word 'galaxy' is derived from the Greek word galaxias which means "milky", it is a reference to our own galaxy the Milky Way.
The Milky Way's nearest neighbour is the Andromeda Galaxy which is about 2.5 million light years (that's 15 million trillion miles) away. In about 4.5 billion years' time, the Milky Way is expected to collide with Andromeda.