Decasyllable

Decasyllable is a term used in syllabic verse. It means a line of ten (10) syllables.

Iambic pentameter, the verse most commonly used in English, is (normally) decasyllabic.

Line lengths in syllabic verse
8 - Octosyllable

10 - Decasyllable

11 - Hendecasyllable

12 - Dodecasyllable