The defining characteristic of an arithmetic sequence is called the common difference. This just means that the difference between each term and the previous term is a constant. It has the form:
a(n)=a+d(n-1), a=initial term, d=common difference, n=term number....
The defining characteristic of a geometric sequence is called the common ratio. This means that the quotient between each term and the previous term is a constant. It has the form:
a(n)=a*r^(n-1), a=initial term, r=common ratio, n=term number.
So in even simpler terms, an arithmetic sequence is a linear sequence and a geometric sequence is an exponential sequence.
