An ELT Glossary : Contrastive Stress

Definition : Stronger emphasis (increase in loudness, length, higher pitch) on one syllable in order to contrast it with another and therefore to "correct" an assumption or implication in another part of the discourse. 

Example: Did you ask Mr Evans? / No, I asked 'Mrs Evans - with contrastive stress on /mɪs/

Extra information : Understanding and producing contrastive stress can be difficult for learners who don't use it in their own language - eg Italians