形式语义（formal semantics） 在编程语言语法中为有效字符串分配计算意义，是 形式语言 的一部份。形式语义 描述了计算机执行程序的过程，具体而言就是输入、输出之间的关系，或者程序在特定平台执行的流程。
In programming language theory, semantics is the rigorous mathematical study of the meaning of programming languages. Semantics assigns computational meaning to valid strings in a programming language syntax. It is closely related to, and often crosses over with, the semantics of mathematical proofs.
Semantics describes the processes a computer follows when executing a program in that specific language. This can be shown by describing the relationship between the input and output of a program, or an explanation of how the program will be executed on a certain platform, hence creating a model of computation.