The Replacer's progress indicator appears when multiple code blocks need to be replaced with a new block and your confirmation is needed for each entry. For instance, if you use the Introduce Constant refactoring to create a new constant from a reference value you will be asked for confirmation before each occurrence of the specified value is replaced with the introduced constant. (Note that this is the default behavior, but you can change it using the refractor's options.)
The progress indicator shows the string that will replace the selected one, indicates how many entries still need to be processed and allows you to do the following:
If you choose to suspend replacement, a window allowing you to resume the operation is displayed in the top-right corner of your IDE window. You can continue working and resume the operation later or close this window by clicking its close button.
The Text Replacer folder in the IDE | Shortcuts page of the Options dialog.