A vacation during which a person engages in activity that is the same as or similar to his or her usual employment: “Our Spanish professor had a busman's holiday this year; she spent her entire vacation doing research in Spain.”
Free time spent in much the same pursuit as one's work. For example, Weather permitting, the lifeguard spent all her days off at the beach—a real busman's holiday. The term alludes to a bus driver spending his day off taking a long bus ride.
[ Late 1800s