Nesting functions in Excel refers to placing one function inside another. The nested function acts as one of the arguments of the main function. The AND, OR, and IF functions are some of the better known logical functions in Excel that are often used together.
Excel: IF Function Combined with AND and OR Functions by Chris Menard
When using the IF, AND, and OR functions, one or all of the conditions must be true for the function to return a TRUE response. Otherwise, the function returns FALSE.
For the OR function (see row 2 in the image below), the function returns TRUE if any of these conditions are true. For the AND function (see row 3), all three conditions must be true or the function returns TRUE.
In the image below, rows 4 through 6 contain formulas with the AND and OR functions nested within the IF function.