"Open Call" or "Open Audition" is an industry term meaning "Anyone can audition." Shows like "American Idol" and "America's Next Top Model" are great examples of having open auditions.
Usually an open audition is
announced through the media and is held on a specific day
or weekend, depending on the project and the turnout. Obviously
an open call for the next "Harry Potter" movie will have
a bigger turn out than a cable access show, but the rules
are all usually the same.
A date is released through a press release, radio spot or newspaper about a specific project. It would say something like, "Open call audition for new talent. If you are male, 18-25 and live in the Los Angeles area, open call auditions will be held for John Doe's upcoming film "My Next Big Movie".
It will then tell you the date,
time and location. A lot of producers and casting directors
use open call auditions to find fresh talent and new faces.
Open auditions also give a person who is casually thinking
about acting, a chance to try out, without needing the experience
or agency help to audition for a role.
If you had fun, and auditioned well at the open call, a casting director may call you back to read again, or perhaps give you another part. The open audition can open many doors and hopefully find you jobs that will give you the experience needed to join the unions like SAG (Screen Actors Guild) or AFTRA (American Federation of Television and Radio Arts.)
Keep an eye out in local papers and trade magazines for open audition advertisements. If you fit the bill, try it out. It can never hurt your career and you never know whose attention you might catch.