The C90 Standard, also known as ANSI C, is a programming language standard established by the American National Standards Institute (ANSI) in 1990. It defines the syntax and semantics of the C programming language, ensuring consistency and portability across different compilers and platforms. This standard includes features like data types, control structures, and standard libraries. C90 serves as a foundation for later standards, such as C99 and C11, which introduced additional features and improvements. By adhering to the C90 Standard, developers can write code that is more likely to compile and run correctly on various systems, promoting better software development practices.