An intensive used to express satisfaction, acceptance, pleasure, excellence, exaltation, approval, awe, or reverence. When used individually, the level of satisfaction expressed is most often directly proportionate to the duration of the vowel sound.
"Mashed potatoes for dinner. Sweet."
"I just won a million dollars? SWEEEEEEET!"
To unexpectedly unleash deep-seated secrets that more-often-than-not delve into the TMI category and leave all those present slack-jawed.
"I don't know WHAT that was! We were just talking about crunchy peanut butter vs. creamy, and all of a sudden she opened the door in the floor and went off about a dog that died 10 years ago, and how different her life would be if she hadn't poisoned it..."