A small gelatine pill size 00 that dissolves in water but not when you put the drug GHB or GBL in it. Therefore it allows you to take a drug that is usually disgusting without having to taste it. This size is 1ml which is half a dose and allows you to control it much better and avoid overdose.
When someone has taken too much of a drug Ghb and it makes them sleep (go on concious)
They normally go in and out of consciousness and its this that is them going into a g hole. Probably derived from K hole.