Rickets is a softening of bones in immature mammals due to deficiency or impaired metabolism of vitamin D, phosphorus or calcium, potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing countries. The predominant cause is a vitamin D deficiency, but lack of adequate calcium in the diet may also lead to rickets (cases of severe diarrhea and vomiting may be the cause of the deficiency). Although it can occur in adults, the majority of cases occur in children suffering from severe malnutrition, usually resulting from famine or starvation during the early stages of childhood.
Osteomalacia is a similar condition occurring in adults, generally due to a deficiency of vitamin D. The origin of the word rickets is probably from the Old English word wrickken ('to twist'). The Greek word "rachitis" (ῥαχίτης, meaning "in or of the spine") was later adopted as the scientific term for rickets, due chiefly to the words' similarity in sound.

General Pediatrics - Malnutrition - 5 - Rickets 2 - Dr.Mohamed El-Komy