What is a busman’s holiday?

The phrase Busman’s Holiday means to do the same thing on one’s day off as one does all week. The accepted origin of the phrase traces it to drivers of London’s horse-drawn omnibuses in the 19th century, who would supposedly spend their days off checking up on how the substitute drivers were treating their horses. In a nutshell, it refers to a vacation during which one engages in activity that is similar to one’s usual work.