A multiple orgasm is when a person has more than one orgasm, in quick succession. People of any gender can have multiple orgasms, although it's more anatomically likely for people with vulvas, as their refractory period is lower.
More About Multiple Orgasms
Having several orgasms with a significant break in between isn't usually considered "multiple orgasms," although many people do need a short time between orgasms when enjoying multiples. When stimulation continues and another wave of pleasure begins, this is considered a multiple.
People with penises can also have multiple orgasms, although it generally requires a little more work and training as it is believed that the male peripheral nervous system is more involved in how the body changes after orgasm. For people with penises, enjoying multiple orgasm may mean enjoying orgasm without ejaculation. Tantric techniques can help teach this. Many people with prostates also find that prostate stimulation can generate a different kind of orgasm, allowing for a multi-orgasmic response.