If some fluid comes out of the penis and the man does not know whether it is semen, urine, or something else – in the event that it comes out with three characteristics: it is accompanied by lust, it comes out with a gush, and one’s body feels weak after it has come out – then that fluid is ruled to be semen; and if none of these three characteristics is present or if even one of them is not, it is not ruled to be semen.
However, in the case of a sick person, it is not necessary that the fluid comes out with a gush or that at the time of coming out his body feels weak; rather, if the only characteristic present is that it comes out with lust, it is ruled to be semen.
As for the fluid that is discharged from the vagina when a woman engages in foreplay or imagines lustful thoughts and which is not enough to dirty other places [such as her clothing], it is pure and does not require ghusl to be performed, nor does it invalidate wuḍūʾ.
However, if the discharged fluid is a lot – to the extent that it can be called an ‘ejaculation’ and it dirties clothing – then in case it is discharged when the woman reaches sexual climax and complete sexual satisfaction (orgasm), it is impure and causes janābah. In fact, even if it is not discharged at that moment, based on obligatory precaution, it is impure and causes janābah.
Whenever a woman doubts whether or not a discharge of fluid was to this extent, or she doubts whether or not fluid was discharged at all, performing ghusl is not obligatory for her nor does it invalidate wuḍūʾ and ghusl.