An expression describing the act of a company using its own products for day-to-day operations.

A company that eats its own dog food sends the message that it considers its own products the best on the market.

This slang was popularized during the dotcom craze when some companies did not use their own products and thus could "not even eat their own dog food". An example would've been a software company that created operating systems but used its competitor's software on its corporate computers.