An ELT Glossary : Elision

Definition : The omission of a sound 

Examples :

-  the pronunciation of chocolate as /ʧɒklət/ rather than /ʧɒkələt/
-  the pronunciation of I don't think so as /aɪ dəʊn θɪŋk səʊ/ rather than /aɪ dəʊnt θɪŋk səʊ/