The Four Titles

It's actually really hard to find a detailed explanation on the Igbo title system. Here's a breakdown of the Igbo political system:

Centralized:

• Type "A" 
• Segmentary Lineages, theocratic kingship, less differentiated title system e.g. Ozo or Eze title, age-grades, and associations e.g. Nri
• Type "B"
• Segmentary Lineages, secular kingship, less differentiated title system e.g. Ozo or Eze title, differentiated title system (hierarchically arranged), age-grades and association e.g. Onitsha, Aboh, Ogwashi, Oguta, Agbor, Issele-Uku
• Type "C"
• Segmentary Lineages, mixed sacred and secular kingship, associations e.g. Aro Chukwu

Middle Range:

• Type "D"
• Segmentary Lineages, Chiefship or headship, less differentiated title system e.g. Ozo or Eze title e.g. Ibagwa Ani
• Type "E"
• Segmentary Lineages, hyper-gerontocracy, less differentiated title system e.g. Ozo or Eze title, age-grades, associations e.g. Ibusa, Illah, Okpanam
• Type "F"
• Segmentary Lineages, hyper-age grades, gerontocracy, less differentiated title system e.g. Ezo or Ozo title, associations e.g. Asaba