A person whose lifestyle is centered on motorcycles, sometimes a member of a motorcycle club.
"After years of working in an office, he traded his suit for leather gear and became a dedicated biker who spends most weekends riding across the state."
In plain English: A biker is someone who rides motorcycles for fun, work, or as part of a group.
"The biker waved to his friends before speeding off down the highway."
Usage: Use this term to describe anyone who rides or lives around motorcycles, though it often implies membership in an organized group rather than just casual riders. Avoid using it as a verb; instead, say someone "rides" a bike if you mean the action itself.
The word biker is formed by adding the suffix "-er" to the noun "bike." It was first used as a shortening of the longer term "motorcycle rider," which itself comes from combining "motor cycle" with the agentive suffix "-er.