A "re-entry" is a track which has previously entered a chart falls out of that chart and then later re-appears in it. This may come about if a release is reissued or if there is a surge of interest in the track. Generally any repeat entry of a track into a chart is considered a re-entry, unless the later version of the track is a materially different recording or significantly repackaged (such as Michael Jackson's "Thriller 25"), where the release would normally be considered separate and thus a "new" entry.