If you're wishy-washy, you're not determined or resolute, but instead act in a way that's weak or uncertain. A politician might give wishy-washy answers to difficult questions, so you're left not really knowing where they stand.
Use the adjective wishy-washy when you describe something that's either wimpy and ineffective or that wavers back and forth without a resolution. You might march up to a bully, ready to give them a piece of your mind, only to end up saying something wishy-washy like, "Um, maybe you could be a little nicer?" Or you could find yourself being wishy-washy as you choose an ice cream flavor, wavering between vanilla and double-fudge mocha with marshmallows.