What is the meaning of irregular?

noun

• A member of an irregular armed force that fights a stronger force by sabotage and harassment.
  • synonyms: guerrilla, guerilla, insurgent
• Merchandise that has imperfections; usually sold at a reduced price without the brand name.
  • synonyms: second

adjective

• Contrary to rule or accepted order or general practice.
  • usage: "irregular hiring practices"
• Not occurring at expected times.
  • synonyms: unpredictable
• Used of the military. ( not belonging to or engaged in by regular army forces)
  • usage: "irregular troops"; "irregular warfare"
• Of solids. ( not having clear dimensions that can be measured; volume must be determined with the principle of liquid displacement)
• Falling below the manufacturer's standard.
  • usage: "irregular jeans"
• Deviating from normal expectations; somewhat odd, strange, or abnormal.
  • usage: "these days large families are atypical"; "atypical clinical findings"; "atypical pneumonia"; "highly irregular behavior"
  • synonyms: atypical
• Lacking continuity or regularity.
  • usage: "an irregular worker"; "employed on a temporary basis"
  • synonyms: temporary
• Of a surface or shape. (; not level or flat or symmetrical)
  • usage: "walking was difficult on the irregular cobblestoned surface"
• Independent in behavior or thought.
  • usage: "she led a somewhat irregular private life"; "maverick politicians"
  • synonyms: maverick, unorthodox