In addition to the male/female genders, there are 3 additional gender subtypes that appear later on in development (for 6 genders total)

Beta: Male or female, no scent glands, and unable to smell the pheromones that Alphas and Omegas emit.

Alpha: Male or female. They have scent glands and are able to show dominance to other Alphas via scent, and by biting and injecting their pheromones into the glands on the napes of omegas, "mark" or "claim" an omega. While under the influence of omega pheromones, a rut may be induced (when Alphas are in a state where they only want to have sex).

Omega: Male or female with an organ (genital cavity) for conception. They have scent glands that give off pheromones and will attract Alphas. In particular, the monthly estrus (which is very similar to a period cycle, or "heats" in other critters) is when omegas are the most fertile and they give off the most pheromones. The effects of estrus can be inhibited by using inhibitors, while pheromone blockers block the pheromones they give off usually. Omegas can be temporarily marked (just bite on glands, bite mark fades), or completely marked (having sex while glands are bit, bite mark stays). Complete marks can be removed via surgery, although it's expensive.

In this story, there is something called a “fit”. Using an equation (of sorts), they would calculate the compatibility between an Alpha and an Omega’s pheromones. The higher the fit, the more likely the two would fall in love and the Omega could be marked. If a fit is too low, the Omega is unable to be marked.

Other terms of note:

False Estrus/Pseudo-estrus: The Omega doesn't go completely in heat (It's likely an off-cycle heat where they show some symptoms, but it's not as bad as a full estrus). This state can be induced via... a variety of reasons, but one reason is the presence of strong Alpha pheromones inducing the Omega into a false heat.

(TN: ... I can't believe I wrote an explanation of omegaverse genders, I wanna hide in a ditch QAQ)