1. In general, the functionality of something refers to the overall quality and how well something performs. For example, a software program may have improved functionality over previous versions with new features and options that were not available in past versions.
2. A function is a group of instructions, also known as a named procedure, used by programming languages to return a single result or a set of results. See the subroutine definition for a full definition.
3. Excel functions are designed to provide one word access to a series of operations. There are several dozen functions and they are organized according to their purposes. For example, in the excel formula "=SUM(A1:A10)", SUM is a function that adds all the numbers in the range of cells specified in the formula. You can go to the Formulas tab (in Excel 2010) or click the formulas button and see all available functions as shown in the example below.