The third trimester in a gestation is the final trimester in a human pregnancy which is usually taken as extending from 28 weeks and 0 days of gestation to term (~38-40 weeks).
History and etymology
Trimester was first seen in English in 1821, a direct borrowing from the French word trimestre, itself introduced from the Latin word 'trimestris' meaning three months, which is derived from the Latin roots, 'tri-' meaning three and 'mensis' meaning month 2.