hi! here to add hatred into the world I am happy to explain that ABO often stands for Alpha Beta Omega where certain types of hermaphroditic people are deeply influenced by seasonal heats and pheromones similar to animals!
Alphas traditionally are the protective muscle, either seen as little more than horny animals, muscleheads, or the ones who run the world!
Betas are regular people like you and me who don't have to worry about heat or ruts and are usually untouched by pheromones!
And Last and usually Least are Omegas! Put most every misogynistic wet dream towards women and put it into some wet mop of a person and you have Omegas! Often regarded as little more than baby machines they are tossed about by the society until circumstance or a big strong Alpha picks them up; deeply affected by pheromones and heat it's not an uncommon trope where a vulnerable omega gets dogpiled by a group of dick-for-brains until their one true love rescues them from the madness!
Thanks to my more well-read friends on the internet for pouring this knowledge out for me to share with you! Have a great day!