Both are used for painting house.
Distemper is also called as cement paint which means it can be directly applied on the wall. It tends to fade in 5 to 6 years. This can be applied inside and also outside the house.
Emulsion gives a finish like oil paint. Oil content is little high in this paint. It gives shinning look for the walls. They little costly as compared to Distemper. It has another variety called exterior emulsion which is used for outside walls of the house. It get faded only after 8 or 9 years.
Distemper has to be given minimum two coats. After it gets faded, entire wall has to be scrubbed (brushed) before start painting. But not in case of emulsion. Coating can be directly given and slightly washable also.