In a normal pregnancy, your ovary releases an egg into your fallopian tube. If the egg meets with a sperm, the fertilized egg moves into your uterus to attach to its lining and continues to grow for the next 9 months. But in up to 1 of every 50 pregnancies, the fertilized egg stays in your fallopian tube. In that case, it's called an ectopic pregnancy or a tubal pregnancy. Refer this link to know more:
http://www.webmd.com/baby/guide/pregnancy-ectopic-pregnancy