What's the difference between a candidate and a confirmed exoplanet?
Confirmed - validated by multiple observations
Confirmed exoplanets are planets that astronomers have proven to a high degree of confidence, using multiple observations and, sometimes, two or more different instruments. Sometimes, further data will cause a confirmed planet to be retracted, but this is a fairly uncommon occurrence.
Candidate - likely discovery, but still needs to be verified
PlanetQuest's list of "candidate exoplanets" comes from the Kepler mission. Kepler has made thousands of likely exoplanet discoveries, but in order for each planet to be considered "confirmed", its existence has to be verified using other instruments, a process that takes time.
As the Kepler team and other researchers across the world sift through the Kepler mission's immense collection of data, it's possible that some candidates will prove to be "false positives" - findings that appear to be exoplanets at first, but later turn out to be the result of other cosmic phenomena.
However, it's very likely that the vast majority of the Kepler exoplanet candidates, especially those in mult-planet systems, are real exoplanets.