Legal Definition of Modification: A change or alteration in matters under discussion and at issue. Modification may take the form of addition or deletion of new elements in the involved issue, but it usually does not change the main thrust of the involved issue or matter under consideration | Learn the legal definition of modification and its importance for business owners. Discover how modifications can be made to contracts, judgments, and business strategies to adapt to changing circumstances. Clear communication and negotiation are key to successful modifications