Differentiate Lap length and development length in RCC member.If they both are different then why do we follow development length as lapping length?

The difference between the two is in the application. A development length is the amount of rebar length that is needed to be embedded or projected into concrete to create a desired bond strength between the two materials. The lap length is the length two rebar pieces must overlap and be tied together to create a bond as if there was no break and the run is "continuous".