In electrical transmission lines, the term loading means the insertion of impedance into a circuit to change the characteristics of the circuit. The loading of a communication ...
http://en.wikipedia.org/wiki/Loading

loading n. A weight placed on something else; a burden. A substance added to something else; a filler
http://www.answers.com/topic/loading

load·ing (l d ng) n. 1. A weight placed on something else; a burden. 2. A substance added to something else; a filler. 3. An addition to an insurance premium.
http://www.thefreedictionary.com/loading

Create easily your own ajax loader icon : Select the type of indicator you want; Enter the background code color you want (tick "Transparent background" if you don't want one
http://www.ajaxload.info/

A loading screen is a picture shown by a computer program, often a video game, while the program is loading or initializing.
http://en.wikipedia.org/wiki/Loading_screen