What is the difference between Additional work and Extra work?

Assume one work is awarded to a contractor on item rate basis. During the execution of work, the necessity arises to do some works which are not given in the contract, but the contractor has been requested to carry out such works and payment will be made after supplemental rates and agreement are executed

This is extra. work

Example Providing stainless steel handrails instead of aluminum handrails

Here extra work is provision of stainless steel handrails

During the execution of foundation work, the quantity given in the agreement is exceeding due to actual type of soil

Here additional quantity of earthwork, filling, RR work will be coming which are needed

Usually in the agreement itself it will be mentioned that the rates are applicable up to 5% more or less besides quantity

Here the additional work comes.