Irregular or not on a fixed schedule; occurring at indeterminate intervals (e.g., services, publications, payments).
この雑誌は不定期に発行されるため、発売日は毎号違う。
This magazine is published irregularly, so the release date differs each issue.
不定期な授業だと学生は予定を立てにくい。
With irregular classes, students find it hard to make schedules.
彼は不定期に海外出張が入ることがあるため、連絡が取りづらい時がある。
He sometimes has irregular overseas business trips, so there are times when he is hard to reach.