A class of novae and cataclysmic variables that have multiple observed eruptions. Their prototype is U Geminorum star. Optically, dwarf nova eruptions have amplitudes of 2-6 mag in V, a duration of a few to 20 days and a recurrence time-scale of weeks to years. Dwarf novae are thought to be semidetached binary stars consisting of a white dwarf primary accreting via Roche lobe overflow from a companion which is usually a late-type, generally main-sequence star. DN outbursts are usually attributed to the release of gravitational energy resulting from an instability in the accretion disk or by sudden mass transfers through the disk.