A shakedown cruise (also known as shakedown time) was an operation where a new starship and her crew tested its systems. It was usually a routine or even a brief ceremonial "maiden voyage", but could also extend to at least one year. A shakedown could reveal flaws inherent in the vessel's construction, especially in prototypes or new technologies.
Examples of shakedowns
The USS Excelsior was called to duty before completion of her transwarp drive. Sabotage rendered the entire mission a failure, and sent the Excelsior back to the shipyard for 2 more years. (Star Trek III: The Search for Spock, Star Trek IV: The Voyage Home)
The USS Enterprise-B was damaged, and one of her guests, legendary Captain James T. Kirk, was lost to the Nexus during the starship's shakedown cruise. Kirk was presumed dead for 78 years until the USS Enterprise-D encountered the Nexus. Captain Jean-Luc Picard discovered that Kirk was still alive inside the Nexus. (Star Trek Generations)
The USS Enterprise-E underwent a one-year shakedown after it was launched. (Star Trek: First Contact)