The memory usage indicator was introduced in screen-scraper 4.5 and shows you how much of the memory currently allocated to screen-scraper that is being used. As screen-scraper requires it, it may be allocated more memory from the underlying Java Virtual Machine, up to the amount specified in the settings dialog box.
In the workbench, the indicator is on the far right of the main window's status bar. In the Enterprise Edition's web interface, the indicator is at the top of the page under the Import button.
The current memory usage can also be queried in a script via the getMemoryUsage method.