Constipation is a delay or difficulty in bowel movement persisting for ≥2 weeks.
It is a common digestive problem, not a disease, and usually not serious caused by changes in diet and early toilet training.
Constipation in children generally first happens in the toddler stage, between ages 2 and 4 years, with studies showing variation in gender-specific prevalence.
Functional constipation is  the one that cannot be explained by any anatomical, physiological, radiological or histological abnormalities.
Organic constipation is with identifiable physiological or organic cause.
Chronic constipation is the constipation that lasts for >8 weeks.