If the call duration is below the expected handling time and the agent dispositions the call with a 'final' result code, the lead will be 'burned' as the system will never call it again. (A final result code is one with the 'Never recall lead – make ineligible’ setting selected on the Recall option of the result code). If the result code is a 'final' with the ‘Do not recall this phone number’ option selected, only the number called for that lead will be burned, not the lead itself.
So, an agent who is dispositioning a call under a minimum user time is usually not waiting long enough to disposition the call. As long as the result code isn't a final result code, the number will be called again.
Another example of a burn: A 'Not Interested' has an minimum handle time set of 30 seconds. If the agent hangs up after 5 seconds as 'Not Interested', you know they didn't try hard enough. You can't possibly tell that someone isn't interested in 5 seconds! They have burned that lead simply because it falls outside the expected handling time set.
So in technical terms, a burn is;
A 'final' result code and NOT a 'Success'
or is 'Wrong Number'
or is 'Not Interested'
and is under exception.