What is the difference between a one-tailed or two-tailed experimental hypothesis?

A one tailed hypothesis, or directional hypothesis, predicts the actual DIRECTION in which the findings will go. It is more precise, and usually used when other research has been carried out previously, giving us a good idea of which way the results will go eg we predict more or less, an increase or decrease, higher or lowerA two-tailed hypothesis, or non-directional hypothesis, predicts an OPEN outcome thus the results can go in 2 directions. It is left very general and is usually used when no other research has been done before thus we do not know what will happen eg we predict a difference, an effect or a change but we do not know in what direction