What is this seasonal reward track called?

A battle pass is this seasonal reward track. It is a paid, time-limited progression system that unlocks a steady stream of rewards, largely cosmetic items rather than anything affecting gameplay balance, as a player racks up playtime or completes challenges over a season, giving people a reason to keep returning to a game they downloaded for free.

A loot crate is a different, often randomized purchase where the reward is unknown until opened, and a season finale is simply the culminating event of a season rather than a purchasable system, so neither matches the guaranteed-reward design of a battle pass.

Combining a battle pass with separately sold cosmetic items lets a game earn steady, recurring revenue from a title that costs nothing to download and sells no actual gameplay advantage, a large part of why the free-to-play model popularized by games like Fortnite became so successful.