Meaning of “irregular” - Learner’s Dictionary

irregular

adjective uk us /ɪˈreɡjələr/
TIME

B2 Irregular actions or events happen with a different amount of time between each one:

an irregular heartbeat
They met at irregular intervals.
SHAPE

B2 not smooth or straight, or having parts that are different sizes:

an irregular coastline
GRAMMAR

B1 not following the general rules in grammar:

irregular verbs/plurals
BEHAVIOUR UK formal

slightly illegal, or not done in the usual and acceptable way:

He led a very irregular life.
irregularity uk us /ɪˌreɡjəˈlærəti/ noun [ C, U ]
irregularly adverb

(Definition of “irregular” from the Cambridge Learner’s Dictionary © Cambridge University Press)