定期: a regular inspection and a three-month commuter pass
Compare next week's planned regular inspection with a purchased three-month commuter pass, distinguishing an occasion, a duration, and ride counts.
An inspection planned for next week
設備の定期点検を来週行う。 says that the equipment will undergo its regular inspection next week. 定期, read ていき, describes the regularity of inspection, with 来週 identifying the planned occasion.
Next week's inspection is not reported as completed. Its exact weekday and a numerically fixed interval between inspections are also unstated.
A pass bought at the station
駅の窓口で三か月の定期を買った。 reports buying a three-month commuter pass at the station counter. 定期 names the pass in 三か月の定期, and 買った reports the actual purchase.
Three months is the pass's duration, not three rides or three passes bought. The exact starting date of that period is not supplied.
The occasion and the pass duration
In the inspection sentence, 定期 qualifies a recurring schedule; at the station counter, it names the pass purchased. 来週 and 三か月 provide an occasion and a duration respectively.
Keep the actual pass purchase separate from the planned inspection. These sentences distinguish inspection and pass contexts rather than asking whether the pass has already expired.
Does 三か月の定期 describe three rides?
Show the answer and why
No. It gives the duration of the pass purchased. Next week in the inspection example is a planned inspection occasion, separate from pass duration or ride count.