Holding down the CTRL (Control) key on the keyboard and clicking the left mouse button. This can be used to select more than one object when the objects are not adjacent to one another. Useful when linking tasks together with the Link Task button or removing links with the Unlink Tasks button. Can also be used in conjunction with the Task Information button to make changes to multiple tasks / resources / assignments. See also SHIFT+Click.
'SOURCE; microsoft project glossary-