The French word jamais usually means “never,” in the negative construction ne… jamais:
On nous dit que les bus ne sont jamais à l'heure.
They tell us that the buses are never on time.
Cap. 11, Cap 24: Les bus sont-ils toujours en retard?
Technically, jamais only means “never” when it’s attached to a ne (though the ne is sometimes dropped in informal speech). An easy way to remember that the French word for “never” is actually two words is to note that “never” is just another way of saying “not ever,” which is the literal translation of ne jamais. But jamais doesn't always have a negative meaning, and sometimes is better translated as “ever.” In fact, as with the word “ever,” there are plenty of instances in which jamais can be used by itself (without the ne) to have a positive meaning.
Cyril uses jamais in this way two times while showing us some of his impressive rollerblading skills:
Si jamais on a envie d'aller skater là-bas...
If we ever feel like going to skate over there...
Cap. 18, Cap 24: Démonstration de roller freestyle
Si jamais is a very common expression that usually is not broken up, like “if ever” is (which is why you have si jamais on a envie instead of si on a jamais envie above, but “if we ever feel” instead of “if ever we feel”).
Another common expression is plus que jamais, “more than ever”:
Les oiseaux sont plus que jamais sous haute surveillance.
More than ever, the birds are under high surveillance.
Cap. 30, Le Journal: La grippe aviaire - Part 1
Don’t confuse this with the negative expression ne… plus jamais (never again), which Charles-Baptiste uses extensively (in an inverted form) in his love song “Sale type” (Dirty Guy):
Plus jamais je ne me couperai les cheveux depuis que tu as mis tes mains dedans
Never again will I cut my hair since you put your hands in it
Cap. 6-7, Charles-Baptiste: Sale type
The opposite of ne… jamais is toujours (always, forever), but sometimes jamais can be used as a synonym for toujours in more formal or poetic contexts (just as “ever” can be a synonym of “always”).
Singer Ina-Ich waxes lyrical with the expression à jamais (forever) in her song “Libre comme l’eau”:
À jamais libre comme le vent
Forever free like the wind
Cap. 55, Ina-Ich: Libre comme l’eau
A similar expression meaning “forever” is pour jamais, which is a more formal version of pour toujours. And if you really want to emphasize eternalness, you can use à tout jamais (forever and ever).
To summarize, let’s take the old adage “never say never” and apply it to jamais: jamais sometimes “says never,” sometimes says “ever,” and sometimes says “forever.” But it never, ever says anything else!