Geometric progression a sequence of the form: $a, ar, ar^2, ar^3, …, ar^n, …$ where $a$ is the initial term $a$ and $r$ is the common ratio
Arithmetic progression a sequence of the form: $a, a+d, a+2d, …, a+dn, …$ where $a$ is the initial term $a$ and $d$ is the common difference
Recurrence relation an equation that expresses $a_n$ in terms of one or more of the previous terms of the sequence