What is the criterion for secretions that take the ruling of سلس ( سلس البول - سلس الريح - سلس الإفرازات - سلس الدم - استحاضة), with their continuous discharge and the permanent dampness of the vulva?

If the discharge is continuous and there isn't enough time for purification (tahara) and prayer, then you are afflicted with incontinence (sals), and similarly if the time of its emission is not regular. However, if these discharges are normal (vaginal moisture), they are pure, and you are required to perform ablution (wudu') for each prayer after its time has begun, and you are not required to purify the spot from them.