They're similar to trigraphs in the C programming language, just an alternate representation of a specific character.

字符实体类似于 C 编程语言中的三联符（trigraphs）：只是特定字符的替代表示。

youdao

Programs he has gone after in the past include agricultural subsidies, defense programs such as C-17 military transport planes, and an alternate engine for the Pentagon's Joint Strike Fighter.

WSJ: Obama to Push New Spending in State of the Union