Relaxed pronunciation, also called word slurring or condensed pronunciation, happens when those syllables are phonetically melded together to create a shortened form of a word or phrase. Yes, this is similar to a contraction. The difference is, contractions such as “could’ve” and “should’ve” are considered part of informal written and spoken language; relaxed pronunciation such as “coulda” and “shoulda,” while part of informal speech, has no standard written form. Now ya know 😉