"Pre-ejaculatory fluid" is the clnical medical way to say what most of us call "pre-cum" or "precum": the usually clear and viscous liquid seceted by the Cowper's Gland (a tiny gland inside the male's genito-urinary works) that precedes actual orgasm and ejaculation of semen ("cum").
The amount secreted as pre-ejaculatory fluid varies from nothing or next-to-nothing to a great amount. See basketball player
The most popular brand of condom-safe sexual lubricant
mimics very well the clearness, thickness (viscosity), slipperiness and slight stickiness of pre-ejaculatory fluid.