Learn English – Unreleased final consonant sounds

pronunciation

In school I learned that unreleased final consonant sounds b,d,d,k,p,t.

My question is what does unreleased mean?

Example:

He played well and ran fast.

My teacher said the "st" in "fast" is unreleased. He said it's because it is joined; so how do I know if the last letters in a word are joined and when they are unreleased?
Simply, my question is how do I know if the word has an unreleased final consonant? How do I know what are they?

Best Answer

From Wikipedia

In most dialects of English, the first stop of a cluster has no audible release, as in apt [ˈæp̚t], doctor [ˈdɒk̚tər], or logged on [ˌlɒɡ̚dˈɒn]. Although such sounds are frequently described as "unreleased", the reality is that the two consonants overlap so that the release of the first takes place during the hold of the second, masking the first consonant's release and making it inaudible

The "st" in "fast" is an odd example - the ones given in the article linked above are better.