N-COUNT (发生几率各半的)相等机会;难以定夺的事 If you say that it is a toss-up whether one thing will happen or another thing will happen, you mean that either result seems equally likely. (发生几率各半的)相等机会;难以定夺的事 [Also + between]
It's a toss-up whether oil prices will go up or down over the days ahead.