Originally Posted by Bionicyle

fred
n.1...a person who spends a lot of money on his bike and clothing, but still can't ride. "What a fred -- too much Lycra and titanium and not enough skill." Synonym for poseur. Occasionally called a "barney".
N.2... a person who has a mishmash of old gear, does't care at all about technology or fashion, didn't race or follow racing, etc. Often identified by chainring marks on white calf socks. Used by "serious" roadies to disparage utility cyclists and touring riders, especially after these totally unfashionable "freds" drop the "serious" roadies on hills because the "serious" guys were really posers. This term is from road touring and, according to popular myth, "Fred" was a well-known grumpy old touring rider, who really was named Fred.

Source: Glossary of Bicycling Slang

I personally like the number 2 definition the best myself, but basically a “Fred” seems to be anyone that doesn’t fit in with someone, or their group in cycling.