Here's why:
* Abstract nouns represent concepts, ideas, qualities, or states. "Trade" represents the concept of exchanging goods or services, which is not something you can touch or physically see.
* It can be used in a general sense. You can talk about "the benefits of trade," or "the history of trade," where "trade" is representing the concept itself, not a specific instance of trading.
However, "trade" can also be a concrete noun depending on the context:
* It can refer to a specific profession or occupation. For example, "He's a carpenter by trade." Here, "trade" is referring to a specific type of work.
* It can refer to a particular exchange of goods or services. For example, "We made a trade for some apples." Here, "trade" refers to a specific act of exchanging.
So, whether "trade" is an abstract or concrete noun depends on its usage in a particular sentence.