It really depends, because there are a few possibilities, and it could be any one or all of them.
Most commonly, that'd just be a woman's usual vaginal discharges.
At nearly any given time, we have vaginal discharges and cervical mucus which are part of our monthly fertility cycle, and also the way the vagina cleans itself. Discharges during phases of the fertility cycle vary, based on the phase that we're in. During one part, they may be thicker, creamier and white, while during others, that mucus is thinner, more clear and more fluid. because the vagina is a self-cleaning organ -- neat, huh? -- we also have discharges which keep everything in balance so that we don't wind up with an infection.
Too, when women become sexually aroused, the vagina often self-lubricates. That fluids tends to be thin and watery, but it also gets mixed with whatever our discharge at a given time is. So, if for instance, you were in the phase of your cycle where your discharge was whiter or creamier, when that got mixed with your self-lubrication, it can appear as a more fluid, whitish discharge.
None of those fluids should smell bad. They have a scent, sure, just like male ejaculate has a scent or sweat has a scent, and that scent can be a little musty, as body fluids tend to be, but not bad.
On the other hand, some vaginal or sexually transmitted infections can also create different discharges which really can smell pretty funky. The discharge due to a yeast infection -- which tends to be white and thick, but also a bit curdly -- for instance, will often smell like yeasty, baking bread. Discharge from a bacterial infection -- which is also whitish and runny, but sometimes is a bit more grey -- tends to smell fishy or metallic. Discharge from certain STIs can also smell different than your normal discharges. So, if you're not up-to-date with your yearly (or more often) pelvic/GYN exams, pap smears and STI tests, you always want to get current with those, even if your discharges look otherwise normal. If you do find, for yourself, that your vaginal discharge starts to smell or look very different than what you're used to, it's always smart to check in with your sexual healthcare provider, even if you HAVE recently had an exam and STI testing.