Mestre corresponds to the mainland area of Venice, in Italy. Although administratively it is part of Venice, from a traveller's perspective it can be considered to be a distinct area. Officially the name "Mestre" corresponds to only one of the boroughs that forms Venice's mainland, but travellers typically consider Mestre as the entire Venice mainland.
Visitors to Venice are often perplexed to see so many tourists and very few locals, and wonder where do the Venetians do live. In fact, most Venetians, including many who work in Venice lagoon's cafes, restaurants, shops and even gondeliers, live in Venice's mainland, Mestre. For most part, Mestre is a normal, modern Italian city with all the conveniences and problems, but not enough to make it a destination on its own. Due to the cheaper accommodation (especially for hotels with 3 stars and above), cheaper parking facilities, and better access to Marco Polo airport, Mestre is often used as a base to explore Venice.