A question about monotonic sequences Are only strictly increasing/decreasing sequences monotonic or can non-decreasing/increasing sequences also be called monotonic ?

We define a sequence monotonic increasing when $a_{n+1}\ge a_n$ holds and strictly monotonic increasing when $a_{n+1}> a_n$ holds. Therefore the case monotonic increasing includes the case strictly monotonic increasing.

See also the related: Difference between Increasing and Monotone increasing function