This is found in the HELP file.
CTRL+SHIFT+ENTER Enter a formula as an array formula
About array formulas and how to enter them
An array formula can perform multiple calculations and then return either a
single result or multiple results. Array formulas act on two or more sets of
values known as array arguments. Each array argument must have the same
number of rows and columns. You create array formulas in the same way that
you create other formulas, except you press CTRL+SHIFT+ENTER to enter the
formula.
