When does the third trimester start?

Stacie β€’ Mother to Ben πŸ‘¦πŸ½, Bash πŸ‘¦πŸ½, and Braxton πŸ‘ΆπŸ½, 420 enthusiast πŸ”₯πŸ’¨, lover of life 😍🀘🏾
I'm 28 weeks exactly today! Am I considered to still be in the second trimester or have I finally made it to the third trimester?