river bed (river beds plural) , riverbed A river bed is the ground which a river flows over. n-count. up-river, upriver. Something that is moving up-river is moving towards the source of a river, from a point down the river.
In economics, the term trade-off is often expressed as an opportunity cost, which is the most preferred possible alternative. A trade-off involves a sacrifice that must be made to get a certain product or experience. A person gives up the opportunity to buy 'good B,' because they want to buy 'good A' instead.
Trade involves the transfer of the ownership of goods or services from one person or entity to another in exchange for other goods or services or for money. Possible synonyms of trade include  commerce  and  financial transaction . A network that allows trade is called a market.