Encumbrance

encumbrance, n., D&D-ism 1. in general usage, something that weighs down or burdens; from Middle English encombren, from Middle French encombrer, from en- "to cause to be" + combre "dam, weir"; c. 14th c. 2. in Dungeons & Dragons, rules to determine the weight and bulkiness of an adventurer's possessions. 3. in tabletop and computer RPGs, a value to determine (1) the maximum number or weight of possessions and equipment a charactermaycarry and (2) how said encumbrance slows the character's movement and/or affects health and causes weariness. 
Ex: "Sir Goodalot can't pick up the Ring of Ethnic Cleansing -- he's maxed out on his Encumbrance. You'll have to drop something."[GJ1] 
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Addendum: Also known as the first rule usually pitched out the window by GMs and players who don't want to bother with bookkeeping everything in their packs. This can tend to ludicrous abuse; characters toting around multiple magic weapons while in full armor and thousands of gold pieces in their pockets.