A purposefully misspelled variant of "period" signifying to end someone's statement/discussion, or to agree with someone. The "T" is used to add emphasis and to mimic certain accents.
Kaiehgla: There will be another Jungkook.
Hailleigh: Periodt, sisterrrr!
Jessicah: Omg, this convo is over, periodt.
A response that shows disappointment whenever somebody says/does something stupid.
Joe: Why are you at your house?
Joe: I just ate soap, and now I'm gonna be famous.