Street score is a valuable or useful item found on the street or in the trash.

Street score指在街边或者垃圾堆中无意发现的有价值或者有用的物件，谓之“街边偶得”。

The word score is here used as a laundered version of a criminal slang term that means "goods or money obtained illegally, esp. as the result of a successful crime."

这里的score原本是一个犯罪领域的俚语，指“作案成功后得来的赃物”，当然，这里是已经“洗白”的用法。