long pants; trousers
Refers to full-length pants, as opposed to shorts (半ズボン). Common in everyday speech.
It's cold today, so I'll wear long pants.
The school uniform includes long trousers.
長ズボン (full-length trousers) is the opposite of ショーツ when ショーツ means short pants.
長ズボン means long pants/trousers, the direct opposite of the short-length 短パン.
Formed from 長, “long,” and ズボン, “trousers.” The ultimate European source of ズボン is uncertain, though French jupon is often proposed.