Virgin Compression Curve: A soil that has been deposited from suspension and consolidated to some stress, clearly the maximum stress to which the soil has ever been subjected, is said to be normally consolidated, and the associated - relationship is termed the virgin compression curve. 
Compression of soil causes largely irreversible movements between particles, so if the soil is unloaded, the resulting rebound curve, or swelling curve, has a flatter slope than the virgin curve and the recompression curve (also called the reloading curve) forms a hysteresis loop with the rebound curve.
Soils now existing under effective stresses smaller than the maximum effective stress at some time in the past are said to be over consolidated.
If the soil is undergoing consolidation down the virgin curve, it is under-consolidated. Obviously, this is a transient condition unless the deposition of sediment is occurring at a fast enough rate that the excess pore water pressures cannot be dissipated.