1. In Latin
The jussive is an “independent” use of the Latin subjunctive. (“Independent” means, a verb in an independent clause, consequently a verb that is not required to be in the subjunctive because of a subordinating conjunction.)
A verb in the 3rd person present subjunctive, jussive function, expresses a command for a third party:
- Veniat! (Let him come!)
- Intrent! (Let them enter!)
A present subjunctive verb in the 1st person plural can do exactly the same the same thing, only then it is called “hortatory,” no doubt because (in the Roman mind) one can give orders for third parties, but only make suggestions for one’s own party.
- Eamus! (Let’s go!)
What about the second person? For that, Latin uses its special imperative forms.
- Veni! Venite! (Come! [singular & plural])
What I call the “Third- (and First-)Person Imperative” in French, is essentially the same as the jussive and hortatory functions of the subjunctive in Latin.
- Qu’il vienne! (Let him come!)
- Qu’ils entrent! (Let them enter!)
- Ô que j’aille à la mer! (Ah, let me go to the sea!)
2. Linguistically Speaking
More generally, as a linguistics term, “jussive” means all means a language has to give commands. In the case of Latin, the jussive would include the two imperative forms and the hortatory and jussive subjunctive. In French, it would include the three imperative forms and and Third- (and First-)Person Imperative.