two terms im having trouble understandiing and wanted to get clarification on. 1. 'Ghost' as in Ghost Commodities. 2. 'Keys' What does this refer to?

Ghost
When someone undercut by more than a certain percentage, the listing is not visible for a while, but can be bought. These are known as ghost auctions.

Keys
When searching, instead of doing an item at a time, you can search for 50 items at once, but will only get back quantity and lowest price. Also the item needs to be included in the addon database or have been seen since the search is based on item id.