na-adjective, noun which may take the genitive case particle 'no', noun
irregular; indeterminate; staggered
Describes schedules, services, payments, or time periods that are not fixed or regular. Often used with nouns like スケジュール, 休み, 支払い, or 間隔.
彼は不定期な仕事をしている。
He does irregular work.
このバスは不定期に
This bus runs on an irregular schedule.
支払いは不定期で、まとめて行われる。
Payments are made irregularly, in a lump sum.
Antonym: 定期的 means regular, periodic, or scheduled.
Compound of 不 (fu, 'not') + 定期 (teiki, 'fixed period'). The reading ふていき follows standard on'yomi.