Appropriate wording for a 50th anniversary party invitation is similar to that of any other party invitation: include the date, time, location and dress code. The type of party determines the exact wording of the invitation, and should give guests a preview of what to expect at the event.
More formal parties require more formal wording. An example of wording for an invitation for a formal event is: "Jill Smith and John Jones request your presence at the 50th vow renewal and anniversary celebration of their parents, Mr. and Mrs. Bill Jones, on July 3rd, 2015 at 7 p.m. at the Liberty Room of the Green Acres Country Club. Black tie reception to follow vow renewal ceremony. RSVP to Jill at 555-123-4567 by June 21st."
For casual affairs, the wording should reflect the more laid-back party tone. These invitations can be creative, cute and fun, as long as the important information is conveyed to the guests. For example, use wording such as "Ain't it nifty? They made it to 50! Bill and Joan have been married 50 years, and we're having a party to celebrate! Join us in the backyard of Jill Smith's house for burgers and dogs on July 3rd, 2015 at 4 p.m. Wear your flip-flops and baseball caps! Text Jill at 555-123-4567 to RSVP or for more info."