Braccae is the Latin term for trousers, and in this context is today used to refer to a style of pants, made from wool. The Romans encountered this style of clothing among peoples whom they called Galli (Gauls). This is often assumed to mean speakers of Celtic languages, though many scholars (including John Collis, Peter S Wells, Stephen Oppenheimer) doubt that the term Galli was primarily based on linguistic affiliation.

Braccae were typically made with a drawstring, and tended to reach from just above the knee at the shortest, to the ankles at the longest, with length generally increasing in tribes living further north.

When the Romans first encountered the braccae, they thought them to be effeminate (Roman men typically wore tunics, which were one-piece outfits terminating at or above the knee). However, braccae eventually became popular among Roman legionaries stationed in cooler climates to the north of southern Italy.

The word is cognate with the English breeches. It appears to derive from the Indo-European root *bhrg- 'break', here apparently used in the sense 'divide', 'separate'. The consonant sequence *b.r.k implies an origin in the Germanic (with regular sound change *g > *k) rather than the Celtic branch of the Indo-European languages; Celtic would regularly have *b.r.g instead, as in Scottish Gaelic briogais. The form *b.r.k is well attested in the Germanic languages (Proto-Germanic *brōkiz, see breeches).