A compatible inkjet cartridge is a brand new ink cartridge manufactured by a third party for use in the brand name it is compatible with.  In other words, an Epson compatible cartridge isn't made by Epson but by a third party meeting OEM's specifications.  What is OEM mean? OEM stands for original equipment manufacturer, in this case, Epson...(cont. below)

Apple Compatible Ink Tanks	HP Inkjet Cartridges
Brother Compatible Ink Tanks	Lexmark Inkjet Cartridges
Canon Compatible Cartridges	Xerox Compatible Cartridges
Epson Compatible Cartridges (Not Genuine Epson Brand)

Download Compatible Cartridge Catalog (32 Kb)

What is a compatible cartridge (cont.)?

...Will using compatible cartridges void my warranty? No, using compatible or remanufactured cartridges will not void your printer's warranty.   Thanks to the Magnuson-Moss Warranty Improvement Act, a company cannot sell a product under the pretense that the consumer must purchase replacement parts, add-ons, etc., from that particular company.

Magnuson-Moss Warranty Improvement Act
United States Code Annotated
Title 15 Commerce and Trade
Chapter 50 Consumer Product Warranties 15 Section 2302

"(c) No warrantor of a consumer product may condition his written or implied warranty of such product on a consumer's using, in connection with such product, any article or service (other than article or service provided without charge under terms of the warranty) which is identified by brand, trade or corporate name; except that prohibition of this subsection may be waived by the commission if:

1) Warrantor satisfies Commission that warranted product will function properly only if the article or service so identified is used in connection with warranted product, and

2) Commission finds that such a waiver is in public's interest."
 

Misterinkjet's Non-OEM Products: Compatible ink cartridges, refill kits and bulk inks do not come from Epson and are not made by Epson.