Some questions do not have one answer. They have an answer per option — per price, per launch date, per bundle.
What a choice variable is
A dimension worth varying. Price, timing and bundling are the common ones.
When a task carries one, the work is built once as a baseline and then once more for each alternative setting, so you can compare like with like instead of reading three separately-argued cases.
Variants
Each built alternative is a variant. Variants share the baseline, so differences between them are real differences rather than drift.
How many
A directory allows up to three choice variables on one task, and you can lower that — including to zero, which turns variants off entirely.
Each variable adds work, so the cost of a task grows with the number of alternatives you ask it to hold open.
Set this under Choice variables per task in directory settings.
Reading variants
The Index tab has a Variant column, and can group by it.