ex·cur·sion 
(ĭk-skûrzhən)
(ĭk-skûrzhən)n.
1. A usually short journey made for pleasure; an outing.
2. A roundtrip in a passenger vehicle at a special low fare.
3. A group taking a short pleasure trip together.
4. A diversion or deviation from a main topic; a digression.
5. Physics
a. A movement from and back to a mean position or axis in an oscillating or alternating motion.
b. The distance traversed in such a movement.
[Latin excursiō, excursiōn-, from excursus, past participle of excurrere, to run out : ex-, ex- + currere, to run; see kers- in the Appendix of Indo-European roots.]