There are two most common types of jealousy, sexual jealousy and romantic jealousy. Sexual jealousy is more common with men and that's feeling threatened that your partner is interested in someone else sexually or may have sex with someone else or may desire to have sex with someone else.
Romantic jealousy is something women are more like to experience. And that a feeling that your partner is interested in someone else in a romantic way, may want to have a relationship with that person or share intimacy or develop a feeling of love for someone else.
Evolutionary psychologists explain this difference in male and female jealousy in this way. From the time of memorial, men have to guard their mates because they wanted to ensure that the DNA that's passed on is theirs, that the offspring is theirs; therefore, men evolved having this sexual jealousy. They're afraid that someone else may pass on their DNA instead of their own by engaging in sex with their partner.
Women on the other hand were more threatened by romantic feelings that their partner may develop for someone else because they were heavily dependent on our ancestral males for a relationship, for support and help in bringing up their offspring. So they were more in tuned to their partner's developing romantic feelings for someone else. They care a little bit less for sexual liasons because ultimately it didn't matter if their partner had sex with someone else as long as they stuck around and helped them rear their offspring.