From Longman Business Dictionary
substitutionsub·sti·tu·tion /ˌsʌbstəˈtjuːʃən-ˈtuː-/ noun [countableC, uncountableU] when you use or do something new or different instead of something else, or something new that is used or done like thisThere was a substitution of temporary labour for regular workers.
→ product substitution → see also elasticity of substitution