What does inside vs outside dilation mean 🤔

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Today at my OB appointment I'm 33+5 (not my 1st baby actually baby #10) she checked me cause I'm having major pressure down there and I'm high risk with gestational diabetes. I was checked back at like 28wks for contractions and was completely closed. But today she said I'm 1cm dilated on the OUTSIDE and ½cm dilated on the inside 🤔. I've never heard of this before. Of course I know it dosen't mean much right now I'm just curious what the outside/inside thing means lol. I was 5cm dilated 80% effaced last pregnancy at 37+4 had her 38wks. Much appreciated