What is the difference between Sprint and Iteration in Scrum and length of each Sprint

Question

1. Is there a difference between Sprint and an Iteration or one can have Iterations within a Sprint or Sprint is just the terminology used instead of Iteration in Scrum? It will be helpful if someone can throw some light on this.

2. Suppose there are 4 sprints and you have decided the first sprint will go up to 10 days is it required that other 3 sprints should have the same length of the 1st decided sprint's length??.