Terrassa, is a city in the east central region of Catalonia, Spain, in the province of Barcelona, comarca of Vallès Occidental, of which it is the cocapital along with Sabadell.
The name Terrassa may be a corruption of Late Latin terra ix ipsa, evolved into proto-Aragonese as terra-iš-sa, potentially conflated with terra-ès-sà "safe/clean place".
It is the site of Roman Egara, a former Visigothic bishopric, which became a Latin Catholic titular see. Since 2004, it is again the see of a bishopric.
The city is located in the Catalan Prelitoral depression, at the feet of the Prelitoral mountain range and the average altitude of the city is 277 meters above sea level. It is 20 and 18 kilometres from Barcelona and Montserrat respectively.
Terrassa is the third largest city in Catalonia, after Barcelona and L’Hospitalet.