A situation in which the outcome cannot be predicted or a decision between two things is very close. I don't know which team will win. Both have done so well this season that it's a real toss-up. Should I take the entry level position, or go back to school? It's really a toss-up in my mind.
a situation where two or more possibilities are equally likely (often + between ) It's a toss-up between Angela and Moira for the editor's job. (often + whether ) It was a toss-up whether prices would go up or down.