What does the road sign yield mean?

Let's identify first what a Yield sign is. The Yield sign is the only sign on the road (US) that is in the shape of a upside-down triangle with rounded corners, similarly to the stop sign, the stop sign is the only sign on the road that's in the shape of a octagon (has 8 sides).

You'll usually see a Yield sign at an intersection, for instance traffic circles. You're not required to stop at the yield sign but you can if you have too to give way to traffic that doesn't have to stop period. Yield signs are not a sign that you blow through. The yield sign means that "You're not required to stop, but you don't have the right-of-way at this intersection." The yield sign is also less restrictive than the stop sign, you still have to give the right-of-way to other traffic, but you're not required to stop at a yield sign.
Just what it says ... "Yield" to oncoming traffic either from behind or in front of you. Many intersections have a yield sign on the right turn asking those vehicles to yield those already on the roadway.