The act of squeezing your legs together (sometimes easier if you cross the legs at the thighs) and tensing the
gluteus Maximus in a rhythmic pattern
to the point of orgasm. This can be achieved by males and females. Males can orgasm and ejaculate from this. Also the penis need not be hard to
accomplish this and both sexes can achieve multiple consecutive orgasms this way. If the penis is squeezed between the thighs hard enough or if the thighs are squeezed hard during and after orgasm, males can hold back ejaculate.
source : male, experience