What is the difference between anterior/posterior anal fissure and lateral anal fissure? What is considered abnormal in terms of anal fissure location

Posterior / anterior. Most "normally located" fissures are due to passage of hard, dry stools or explosive diarrrhea. These are almost exclusively posterior in men but can be anterior in up to 10% of women. These respond well to lateral internal sphincterotomy. Secondary anal fissures are associated with crohn disease, leukemia and certain other neutropenic blood conditions. Surgery should be avoided.
Big difference. Anterior and posterior anal fistula are almost always caused by trauma - forceful bm due to constipation. Lateral fissures are caused by crohn's disease, sexually transmitted disease and cancer, and need to be biopsied. You should see a general surgeon or proctologist.