ELI5 Bicycles - Why are women's bike frames different to men's?

Why do typical female bike frames have a dip in the frame, while men's have a horizontal beam? Why is the geometry of a racing bike slightly different from that of a typical bike? How about mountain bikes vs road bikes? What is gravel biking?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: wharrgarblll, robobenjie, iwasnotarobot, decade240 & brainflakes   To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Facebook: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]