Here's one way to look at it.
AC is alternating current. And while you need a voltage to drive that current, let's first look at it as its name implies. In AC, the direction of current changes with respect to time. That means electrons might flow from left to right in a wire for a second, and then from right to left for a second, and then left to right, and on and on. How quickly the current changes direction is called frequency.
Lets say we attach a load (a resistor for instance) up to an AC source. (Look at my attached drawings.) If the direction of current is downwards through the resistor, then the voltage on the white wire must be positive with respect to the black wire. This is because current flows from high potential (voltage) to low potential. Similarly, if the direction of current is upwards through the resistor, then the voltage on the black wire must be positive with respect to the white wire. This is exactly the same as saying the voltage of the white wire is negative with respect to the black wire.
That kind of introduces the ideas of a reference node, or "ground", or "0V" or "-". If we make all of our measurements with respect to the black wire, then the voltage on the white wire will alternate between positive and negative values. This is because we lock down the black wire as the 0V reference point of the circuit. All other measurements in the circuit must be referenced to it (i.e. put the black lead of your multimeter on the reference node and make all voltage measurements with respect to it.)
Maybe that's all very confusing, still..
So to answer your question, no, AC does not have a + or -. You can get really philosophical when you start talking about the existence of "ground" or "-" (or whatever). But for your purposes, if you hooked up an AC voltage to the + and - rails on a breadboard, then 50% of the time the markings on the breadboard are going to be correct (when current flows out of the + terminal and back into the - terminal). But the other 50% of the time, current will flow from - to +, which is the opposite of what the markings suggest.