Free Memory allows you to free up runtime memory on your iPhone or iPod Touch.
The iPhone or iPod Touch comes only with 128MB of runtime memory. This is not to be confused with the storage memory which is usually 8GB, 16GB or 32GB of persistent memory.
The iPhone or iPod Touch OS does not implement virtual memory, so this means that the OS does not make use of the storage memory to increase the size of memory available to running applications.
Some native applications that come with the iPhone continues to run even after you have closed them, for example, the iPod player, Phone application, Mail application and the Safari web browser.