Deep structure refers to the underlying grammatical structure of a sentence that conveys its core meaning, regardless of how it is expressed. This concept, introduced by linguist Noam Chomsky, helps to explain how different sentences can share the same deep structure while differing in surface structure, which is the way sentences are actually spoken or written. In linguistics, deep structure is crucial for understanding the relationship between syntax and semantics. It allows for the analysis of how various languages can express similar ideas through different word orders and grammatical forms, highlighting the universal aspects of human language.