Capable of changing or of being changed. With reference to operating systems, the implication is that the system is capable of changing while it continues to run. As an example, the total amount of memory available may be defined by the contents of a word within the operating system. If this word can be altered without stopping the system and reloading a fresh copy of the operating system, then it is possible to alter dynamically the total amount of memory on the system.
With reference to programming, the adjective is applied to operations that take place while a program is running, as compared with those that take place during the compilation phase. For example, dynamic arrays are allocated space while the program is running.
Compare static.