Uday,

If I understand the question correctly, it is essentially the difference
between the cooling load of the space and the capacity of the equipment
needed to meet that load.

For example, a space load is based on internal and external heat gains and
ventilation required to maintain conditions in that space. The equipment
that supplies that load will have a greater capacity as it must also
account for external loads not associated with the space load. This includes
the effects of treating outdoor air (moisture and temperature) as well as
other factors including heat losses (ducts) and heat generated by fan
motors, etc. The capacity at the equipment, or what is needed as it leaves
the coil, is called the coil load.

I hope this helps,

Jeff Ross-Bain, PE, LEED AP BD+C, BEMP