A "Briner" is a fan of the cable television host and cook Alton Brown. Originally it referred to fans of Alton's show Good Eats but now can refer to fans of Feasting on Asphalt and Iron Chef America as well. Specifically it refers to participants on the message board at www.goodeatsfanpage.com. The name refers to Alton's technique of soaking turkeys and other meats in a flavorful salt solution to enhance their flavor, a technique called "Brining", hence "Briners".
If you can name all the different parts of the inside of an egg and argue furiously about sugar in cornbread or the presence of beans in Chili (with an I), you might be a Briner.