Recurrent novae are thought to arise in the same way as classical novae, through a white dwarf in a close binary system accreting a surface layer of hydrogen from a main sequence companion. Once the temperature at the bottom of this hydrogen layer reaches about 10 million Kelvin, a runaway thermonuclear reaction takes place which ejects the unburnt hydrogen into a rapidly-expanding shell around the white dwarf. This is the nova outburst.
While classical novae have only been seen in outburst once, recurrent novae have undergone at least two outbursts over the past century (since astronomers started taking notice!). The time interval between outbursts varies from 10 to 100 years, and astronomers propose that classical novae will be seen as recurrent novae given enough time.
The 8 recurrent novae astronomers know about tend to be slightly brighter than classical novae in their quiescent state. In outburst, they have the same brightness or are slightly fainter than classical novae, with the brightest maxima occuring for those novae with the shortest time interval between outbursts.