live load

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A moving, variable weight added to the dead load or intrinsic weight of a structure or vehicle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun roofing Temporary load that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, snow, ice or rain, etc.)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a variable load on a structure (e.g. a bridge) such as moving traffic