On-Vacation-In-Vacation | Commonly Confused Words

On vacation

/ɒn vəˈkeɪʃən/

A period of time when someone is not at work or school, typically used for travel or relaxation

/ɪn veɪˈkeɪʃən/

A phrase meaning to be away from work and other daily responsibilities, usually for rest or travel.

On vacation is used to describe a period when someone is taking time off from work or regular activities, typically involving travel or relaxation.
Think of on vacation like being on a journey or adventure, not taking part in the regular routine.
In vacation is not a commonly accepted phrase in English; on vacation is the correct usage.
Remember that on vacation implies a break from usual duties with the emphasis on the activity or state of being away.
On vacation is analogous to on leave, where on signifies being in a state of doing or experiencing something.