问一个比较小白的问题，论文里delay用O（）表示是怎么回事

先贴一段相关的论文，第一次见到这样的定义和表达形式，请论坛老手路过指点一下，google好久都没有相关资料，难道是数学某个函数的表达式?
论文片段如下
There are many cases where it is desired to add more than two numbers together. The straightforward way of adding
together m numbers (all n bits wide) is to add the first two, then add that sum to the next, and so on. This requires
a total of m − 1 additions, for a total gate delay of O(mlg n) (assuming lookahead carry adders). Instead, a tree of
adders can be formed, taking only O(lgm · lg n) gate delays.

google "big o"

   表示数量级，在分析算法复杂度时常用到。找一本讲算法的教材，前几章肯定会介绍它。

   谢谢二楼和三楼的兄弟了，三楼的前辈能推荐本算法书吗?