<human>:  Explain the mathematical concept of a limit.
<bot>: A limit is a mathematical concept used to describe the behavior of a function or sequence as it approaches a particular value or point. In other words, it is used to describe what a function does as it gets closer and nearer to some value. There are two types of limits: the left-hand limit and the right-hand limit. The left-hand limit describes what the function does as it approaches the value from below, while the right-hand limit describes what the function does as it approaches the value from above. The left limit and the right limit together define the behavior of the function or sequence as it approaches the value. For instance, the limit of f(x)=x² at x=3 is 9, because no matter how close you get to 3 (from below or above), the value of this function is always 9.