"Vendor Trash" is a derogatory term used to describe items which serve no purpose other than to be sold to in-game stores for money. This mainly occurs in RPGs, and MMORPGs; the most well-known type of vendor trash is extremely poor quality equipment, dropped by enemies in low-level areas, such as a sword that does less damage than the one warriors start with, or a "broken" chestplate that only adds 1 or 2 to a player's armour level. These items are only "useful" to absolute beginners who do not have anything equipped to that item slot yet.
Another, slightly more recent type of vendor trash takes the form of items which are literally useless other than their value to vendors, implemented to avoid the related issue of inappropriate loot, where, for example, an ordinary wolf will inexplicably be carrying gold coins, or a giant spider will have an enchanted bracer on them. This second type of trash would have wolves drop wolf pelts or claws, items which cannot be used for any purpose, but which can be sold for money to vendors. Although this adds a step to the cash reward process (and takes up a slot in your inventory), it is slightly more realistic than a wild animal carrying money. Of course, this brings up the question of why exactly a blacksmith would want to buy broken spider legs and venom glands, but it's really best not to think about these things.
Some games feature systems to streamline the vendor trash process in various ways. For example, the Xbox game The Bard's Tale and the later, much more popular Dishonored both feature systems where instead of having to carry vendor trash around until you get to a store, such items are converted into their monetary value the instant you pick them up, so that instead of carrying around spools of copper wire or bottles of hemlock essence, Dishonored's Corvo Attano is given small payouts of cold, hard cash right there on the spot, to represent him having sold them later on. The comedy-RPG Deathspank and its sequels include a parody of this concept; instead of having any stores at all, the heroic Deathspank earns money by putting useless items and items he doesn't need into a meat grinder in his inventory, which destroys the items and somehow converts them into gold coins.
Although "vendor trash" is an inherently derogatory term, and it generally refers to broken equipment and animal body parts, some games feature items with no purpose other than as valuable trade commodities that take the form of rare and expensive items. For example, Resident Evil 4 and 5 feature valuable gems and treasures lying around its levels which can be sold at the store for more money to buy items. Similarly, in Dead Space, Isaac Clarke can retrieve electronic semiconductors made from rare materials ( gold, ruby, and diamond) to cash in at the USG Ishimura's Store kiosks.