Definition
to purchase an item, often a house or car, that is either more expensive or less costly than what you currently possess
購買價值更高或更低的物品（通常指房屋或汽車）
They decided to sell their old car and then purchase a new luxury sedan, referring to the process as trading up.
他們決定賣掉舊車，然後買一輛新的豪華轎車，並稱這個過程為升級。
Due to the poor economy, they opted to trade down from their large house to a smaller apartment, which is what they referred to as trading down.
由於經濟不景氣，他們選擇從大房子搬到較小的公寓，並稱這個過程為降級。
In the market, people often decide to trade up or down their homes to meet their current needs.
在市場上，人們經常決定升級或降級他們的房屋以滿足當前需求。