A series is the
sum of the numbers in a sequence.

For example the series 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 is
formed from the first ten odd numbers, and its sum is 100.

Similarly
the series 1 + 2 + 4 + 8 + 16 + 32 is formed from the first six terms
of the powers of 2, and its sum is 63.