The document discusses arithmetic sequences, which are number sequences where each term is calculated by adding the same number, called the common difference, to the preceding term. It provides examples of arithmetic sequences like 16, 48, 80, 112, 144 where each term is found by adding 32 to the previous term, making 32 the common difference. Another example is the sequence 2, 5, 8, 11, 14 which has a common difference of 3.