Hi viz means just that, clothing to make you highly visable normally day and night. So high viz will normally have silver reflective panels AND flourescent panels (typically yellow or orange. . .Though you can get pink too).
Lots of relective belts etc, Sam Brown belts and the like are reflective & flourescent colours. Though not all reflectives flourese (silver, green, blue and red relectives dont flourese)
reflective means it reflects light, so requires a light source (headlight, torch etc) to be shone,
flourescence occurs when UV reacts with the colouring to cause a glowing effect. Normally the UV is from daylight, so after the sun sets it is next to useless.