In my Elementary Social Statistics course, we are currently studying hypothesis testing for 1 and 2 sample cases. In the section about 2-sample cases, there is mention of the "pooled estimate" which I don't quite understand the concept of. The definition I have here is "the standard deviation fo the sampling distribution of the difference between sample means/proportions." I understand it to be similar to the Central Limit Theorem, as I have a note written below this definition that says "Sampling distribution that would occur if we took repeated samples of both populations and subtracted values of sample 1 - sample 2. Each difference becomes a point on the distribution and will approach normal [as the N increases]." I'm still not entirely understanding this concept. What is the pooled estimate explained in more simple terms?