[rahimnathwani]

If you've used pivot tables in Excel or Google Sheets, you'll know that you have:

A) rows and columns

B) values

Dimensions are things you might include in A.

Facts (or measures) are things you can aggregate, and would be part of B.

In the old days, you often couldn't quickly (on demand) compute the answer to a question, due to memory and processing limitations.

But, if you could decide ahead of time what dimensions and facts you wanted, you could compute all the little slices, e.g. value of sales in the north region by salesperson Bob in month July 1996.

Then, when you needed some particular pivot table, your software could provide it to you just by summing these precomputed slices.

The OL in OLAP stands for 'online', i.e. you'd do your analytical processing ('AP') live, rather than waiting for some long-running batch job.