What is Irregular ?
Irregular is (adj) 1. not happening in a regular way An irregular pattern of lines and circles. His heart had an irregular beat. 2. not level An irregular stone path leads across the garden. 3. not happening always at the same time His payments are very irregular. He makes irregular visits to his mother in hospital. 4. not according to rules or a usual way of doing something This procedure is highly irregular.
source: Easier English, Student Dictionary Upper Intermediate Level