Real time is what we experience in our everyday lives. It flows in one direction, from past to future, and is measured by physical processes like the ticking of a clock or the decay of radioactive particles.
Imaginary time is a mathematical concept used in quantum mechanics and cosmology. It's represented by multiplying regular time by i (the square root of -1). In imaginary time, the distinction between time and space becomes blurred, and time behaves more like a spatial dimension.