It's morning; a girl is at home on a school day because she'd been suspended. Suddenly, a friend of hers appears at her house to give her some homework. To explain why she's here during school time, se says:
"I had a spare so I tought I'd drop it [the homeworks] off."
What does "have a spare" mean exactly in this context?
Just to provide more context: later, the girl that brings the homeworks says:
I have to go. I'm supposed to be doing my online math.