Within many English dialects, it is common to pronounce the word ‘butter’ using a /d/ sound rather than a /t/ sound. This is an example of?

In American English there is no virtually no distinction between saying "butter" and "budder." So, yes, there are dialects within English where t will sound like d in a word like "butter."

Hello Bentarzi,

I am British and it is extremely rare that I hear someone pronounce butter as 'budder', although I know a few people do pronounce it as budder.

Poseidon

I'm not sure exactly what the question is looking for, but "lenition" is one correct answer.

No idea of the official name, but the Brother's Grimm identified it.