number that is the difference between consecutive terms in an arithmetic sequence. The difference between a term and the previous term is always the same value.
number that is the ratio between consecutive terms in a geometric sequence. The ratio between a term and the previous term is always the same value.
sequence of numbers in which each term is found by adding the two previous terms. The first several terms of the sequence are 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ….
abbreviated way of writing a sum that uses the Greek letter sigma. is read as "the sum of sub as goes from 1 to 9."