Memory allocation is the process by which a computer program requests and receives memory space from the operating system. This space is used to store data and instructions while the program is running. Memory allocation can be dynamic, where the program requests memory as needed, or static, where memory is allocated at compile time. When a program is executed, it may require different amounts of memory at different times. Dynamic memory allocation allows for flexibility, enabling programs to use only the memory they need, which can improve efficiency. However, improper management of allocated memory can lead to issues like memory leaks or fragmentation.