So confused!

So, I always thought that the first trimester ended at the end of 13 weeks and that the second began at 14. However, some sites say 12, some say 13 some say 14. The hospital I work at says <14 is first trimester and >14 is second. So I decided that 14 it is. Well then today at my 11w4d appointment my doctor had a chart posted saying that 1-16 weeks is first trimester and starting at 17 it’s the second trimester. So what do you guys go by? Is week 13-17 some kind of thing pregnancy limbo? 😂