ID:
The unique identifier for the loottable

Name:
This is not used in the server any place; it's just there to make the database more human-readable. Usually the loottable name is the same as the name of the npc with the loottable, but it doesn't have to be.

mincash:
The minimum about of cash the mob will drop when killed. An entry of "1" would set 1 copper as the minimum cash drop. An entry of "54321" would set 54 plat, 3 gold, 2 silver, 1 copper as the minimum cash drop. As far as I know, there currently is no way to make a mob drop more than 9 copper, silver, or gold at a time.

maxcash:
The maximum amount of cash the mob will drop when killed. The format is the same as for mincash. When the mob spawns, the server generates a random value between the mincash and maxcash, and the random value is assigned to the mob's loot.

avgcoin:
No one seems to know what this field does, and there are actually 0 loottables in the ProjectEQ database that use this field. Leave it set to 0 if you want a normal "pick an amount between mincash and maxcash" cash drop for your mob, as changing it from 0 will cause erratic results.