Definitions for walk-on
Random House Webster's College Dictionary
a small part in a play or other entertainment, esp. a part without speaking lines.
Ref: Compare bit2 (def. 4). 1 2 6
an athlete trying out for a team who has not been drafted, specifically invited, or awarded a scholarship.
Origin of walk-on:
plays a small part in a dramatic production
not capable of or especially not involving speech or spoken lines
"had a nonspeaking role in the play"
A student athlete that wants to try out for a college sports/athletic team without the benefit of a scholarship or having been recruited.
An actor of a small (or "bit") part in a theatrical production or film, often without speaking lines.