The name Terrassa derives from Latin Terracia, either from earlier Terracium castellum (“earthen castle”),[3] or meaning "terrace", "area of flat land".

Terrassa's location as the most-inland city in the Barcelona Metropolitan Region makes it sometimes be referred to as the "entrance to Central Catalonia".

Terrassa is also the largest municipality in what's considered the second most important urban, economic and cultural center of Catalonia, the Vallès region.

Terrassa originated as the Roman town of Egara (Municipium Flavium Egara), which was founded during the time of the emperor Vespasian (69–79 CE), alongside the torrent of Vallparadís (nowadays an urban park) close to the Iberian town of Egosa, on the site of which some ceramics and coins have been found.

[7] Other important remains from the Middle Ages are the former cathedral, the castle of Vallparadís (from 1344 to 1413 a Carthusian monastery and today a municipal museum) and the tower of the castle-palace of the count-king.

Particularly notable Modernista buildings include the Masia Freixa (1907), the Vapor Aymerich, Amat i Jover textile mill (1907) (now the Museum of Science and Industry of Catalonia), the Principal theater (1920), the city hall (1902), the Alegre de Sagrera house/museum (1911), the Industrial School (1904), the Gran Casino (1920), the Parc de Desinfecció (1920), and the Independència market (1908).

[9] The episcopal see of Ègara already existed by about 450 CE, when it was established on territory split off from the Roman Catholic Diocese of Barcelona, under the Metropolitan Archdiocese of Tarragona.

It effectively succumbed to the Arab (Muslim) conquest in the 8th century and was probably suppressed, its territory being (rather nominally) returned to the Diocese of Barcelona.

After the Catholic Reconquista of the region in the tenth century, the see was not restored, its territory being incorporated in the (mother) diocese of Barcelona.

Why a request to restore the bishopric by its Metropolitan of Tarragona, Cesareo, wasn't honored by Pope John XII (955–964) is unclear.

There is also an altar stone dating from the 10th century and medieval and Romanesque tombstones (one of which documents the name of the Roman town of Egara).

The city is heir to a rich medieval, Modernista and industrial legacy, and possesses an extensive network of libraries, historical archives and museums.

A lot of musicians and actors are based in Terrassa because of the large number of music schools, a long amateur theater tradition and the local seat of the Institut del Teatre.

Since 1982, the Terrassa Jazz Festival has been especially outstanding, with guests like Stan Getz, Chet Baker, Dexter Gordon, Tete Montoliu, Dizzy Gillespie.

Compared to other cities its size, like Sabadell or l'Hospitalet de Llobregat it houses a significant number of colles (groups) of different catalan cultural traditions.

Terrassa is the home and birthplace of FC Barcelona and Spain national football team midfielders Xavi and Dani Olmo.

On 22 November 2015, Terrassa's Plaça Vella was the scene of the world's first successful 4 de 10 amb folre i manilles, completed by the Minyons.