I found this on the web, it doesn't list Poor as a Grade.
Good (G) - Heavily worn. Design and legend visible but faint in spots.
On some coins, full rims are not required for this grade. You must be able to read the date and mint mark.
Almost Good (AG) - Outlined design. Parts of date and legend worn smooth.
This is a used up coin. You should be able to make out the date (possibly with some effort). Often, only parts of the last two digits will be visible.
Fair (Fair) - You can identify the coin as to its type.
There may be holes, it might be bent, or it might just have a LOT of honest wear. You may or may not see the date depending on the type and the nature of the wear. Fair coins are also sometimes called "filler" coins. That is because you can buy them very cheaply to fill the holes in your collection. Otherwise, you might never be able to afford the coin. Many people collect fair condition coins, especially the rarer dates and types. Dateless
Buffalo nickels, for example, are still worth about a dime. Some of the earlier type coins may be worth $50 or more in fair condition.
Basal State (Basal) - You can identify the lump of metal as being a coin.
Basil state coins have extraordinarily low value. A basil state large cent, for example, might sell for a nickel.