In most ELT writing, rapid delivery is referred to as 'connected speech.'
In linguistics analyisis of pronunciation there are various terms such as:
assimilation - where d sounds next to p, b or m sounds run into each other, like in 'handball'
elision - where you drop the sound of a word, as in 'Christmas' or 'sandwich'
absorption - where the sounds of words run together, as in 'a nice house' - 'an ice house'.
For more information on this try these websites:
Karen's linguistic issues -
Karen's Linguistics Issues A Reference Glossary to Pronunciation Terms and Terminology for ESL EFL TESL TEFL Teacher