A dare is a challenge - usually only used among children or teenagers. For example, two children are walking in a park and come upon an obviously rickety bridge. There is a sign saying "BRIDGE CLOSED" because it is dangerous. One child will say to the other "I dare you to walk across that!" The other child has the option to decline, but unfortunately, in most cases, when someone is "dared" they go ahead and perform the task, no matter how risky.
