Can someone explain what the percentile to me??

Joanna • married 10.11.12 ttc for 2 years. Emma Rosalie 4.16.17 baby#2 est. 8.8.18
My last u/s was when i was 25 weeks and today my for visit he said her growth is good that shes 44 percentile. What exactly does that mean?? I know not to worry, because he said shes right on track, but just want to know what it means lol