Addon(s) are third party programs that can be downloaded to aid in all activities of World of Warcraft. Gold makers are no exception. See my blog post on How i Operate in the Inscription Market. I download my addons from curse.com
Alt, short for Alternative Character, are other characters a player has in operation. For gold makers they are used to carry out gold making activities such as posting items or indeed are maxed out in two further professions. It is the norm for gold makers to have several maxed out professions.
Cancel and repost, a term used by gold makers everywhere where typically an addon is used to automatically cancel items on the Auction House that are no longer the lowest price and then the addon is used to automatically repost all the items at the lowest prices.
Fall back price is the price which an item is posted if no such item already exists on the Auction House. So, for example, if i post a glyph to the Auction House and there is no glyph already posted by a competitor then it gets posted at the Fall back price of 400 gold.
Gold Cap is currently set at 1 copper below 1 million gold and is the maximum amount a single character can hold. A player can of course hold gold over several characters and therefore hold over 1 million gold.
GPH is short for Gold Per Hour and is a much critised measurement of gold making over time to compare various gold making activities.
Guild Bank is a guild that a character is the sole member of for the sole purpose of storing items or raw materials for gold making activities. Every gold maker needs one. See my post on Guild Banks and how to set them up.
Main, short for Main Character, is a players main character in World of Warcraft.
Proc, short "for procedure", is a term commonly used to refer to a special event that occurs whilst undertaking another action. For example, whilst milling cataclysm herbs there is a chance to proc some burning embers. accoring to WoWWiki The term derives from "spec proc" which is short for special proceedure.
Undercut is a term used by gold makers to describe the process of posting items at the lowest price on the Auction House by a specific amount. Typicall undercut amounts are 1 copper or 1 silver.