In MIL-STD-2167A, 'CSCI' stands for Computer Software Configuration Item, which refers to a specific software component or segment that is managed as a distinct entity within a system. 'CSC' denotes Computer Software Component, indicating individual pieces of software that make up the CSCI. 'CSU' is the Computer Software Unit, which is a smaller subset of the CSC that typically encapsulates a specific functionality or module within the software. These distinctions help in organizing software development and ensuring proper configuration management throughout the software lifecycle.