The USS Yorktown was a Federation starship that was in service during the latter half of the 23rd century.
In 2268, the Yorktown was scheduled to deliver vaccines bound for the colony on Theta VII after a rendezvous with the USS Enterprise. (TOS: "Obsession")
In 2286 the Yorktown was under the command of Captain Joel Randolph. While deployed near the Sol system, the Yorktown was one of the many vessels disabled by the Whale probe near Earth.
In Randolph's distress call to Starfleet Command, he noted that the ship had lost all power and that all non-essential crew were given hiber-sedatives to slow down consumption of life support reserves. Meanwhile, the chief engineer attempted to deploy a makeshift solar sail so as to focus and absorb radiation from a nearby sun they were orbiting, with the hopes of generating power to keep the crew alive. (Star Trek IV: The Voyage Home)
In 2293, Tuvok's father was a Starfleet officer serving aboard the Yorktown. (VOY: "Flashback")
Yorktown personnel
Background
According to an article by Greg Jein in a 1970s fanzine regarding starship registries, he assigned the number NCC-1717 to the name Yorktown. This registry has been further propagated by being included in the writings of Michael Okuda, such as the Star Trek Encyclopedia, which also references the Yorktown as a Constitution-class starship.
The Yorktown was listed as a Constitution-class starship, with the registry NCC-1704, in Franz Joseph's Star Fleet Technical Manual. However, much of the information in that manual that wasn't used on screen in some form is considered non-canon.
The USS Yorktown was the name of the central starship in Gene Roddenberry's first Star Trek proposal to NBC in 1964. The ship was named after the USS Yorktown, a World War II American aircraft carrier, which in turn was named after the last major battle of the American Revolution, won in 1781 by a combined Franco-American army commanded by Gen. George Washington.
Gene Roddenberry, in a nod to his original name choice from 1964, suggested that the Yorktown was renamed Enterprise-A at the end of Star Trek IV, explaining why the latter ship seemed to be launched so quickly at the end of the movie. However, there is no direct evidence to confirm this theory. If the NCC-1701-A was refit from a ship from the TOS era, that would mean that the Yorktown was renamed after over 20 years of service -- a seemingly disrespectful violation of starship naming parlance. However, if the Yorktown Roddenberry spoke of was a brand new ship, then why would it have been decommissioned only seven years later in Star Trek VI? Scrapping a relatively new cruiser seems like a waste.
A third possibility is that the Yorktown Roddenberry meant was neither aged nor young: Presuming the TOS Yorktown long-since retired, it could've been replaced by a Constitution ship of the Star Trek Movies-era several years hence. This would mean considering the TOS-era ship and the 2280s ship as two separate incarnations.
If the Yorktown was indeed renamed as the Enterprise-A, then Tuvok's father's ship must be a different Yorktown. However, if you disregard Roddenberry's behind-the-scenes commentary, there is no onscreen evidence that contradicts the three 23rd century mentions of the Yorktown name all being the same vessel.
The FASA sourcebook "Star Trek: The Next Generation Officer's Manual" lists a USS Yorktown (NCC-2033) of this era which belonged to the Excelsior-class, the book however is not considered canon.
In the "Star Trek: The Next Generation" novel "Crossover", the Yorktown is revealed to have become a museum exhibit on a starbase, but its bridge has been replaced with the original bridge of the first Enterprise. In the story in question, Captain Montgomery Scott steals the Yorktown to rescue Spock, recently captured by the Romulans, and fits it with an ancient Romulan cloaking device. The mission proves successful, but aid is still required from the Enterprise-D for Spock, Scotty and the Unification movement to escape.