Definitions

“(..) Under certain circumstances sounds disappear; one might express this in more technical language by saying that in certain a phoneme may be realized as zero, or have zero realization or be deleted.(..) elision is typical of rapid casual speech(..)”

Peter Roach – English Phonetics and Phonology, a course book.

"Some of the sounds that are heard if words are pronounced slowly and clearly appear not to be pronounced when the same words are produced in a rapid, colloquial style, or when the words occur in a different context; these “missing sounds” are said to have been elided."

Peter Roach - A Little Encyclopaedia Of Phonetics

“A type of economy of articulation that consist of omitting either a vowel or a consonant. The omission of sounds is known as elision”

Hector Ortiz Lira – A course in English phonetics for Spanish speakers