When you convert a fraction to a decimal sometimes the decimal repeats forever. For example 1/3 as a decimal = 0.333333333.... (or 0.3 "recurring"). Another example is 1/7=0.142857142857.... (or 0.142857 recurring).
A repeating decimal is a decimal that, well, repeats itself! Like .33333333333333....... The threes never end, they just keep going. Non-reapeting are decimals like .5 or .3 or .57. They end! :)