Small o notation

Small-o notation represents the upper bound of the runtime of an algorithm; the runtime will be strictly smaller than Small-o. It gives the worst case complexity of an algorithm. ¹

If $f = O(g)$ and $g \ne O(f)$, then $$ f = o(g) \iff \lim_{n \to \infty} \frac{f(n)}{g(n)} = 0 $$ It can also be said that f is "strictly less than" $g$.