The password for the user name specified in the Start Service As User property. Leave this property blank if the user name is blank. Note that this password is NOT encrypted when the project is saved. This should not pose any problems, since developers should not hard-code passwords anyway. The end user should be prompted to enter a user name, prompted for the password, then this field should use string resolution to make use of the password entered by the end user. It is resolved at runtime.
See the CreateService Win32 API help documentation. This value is passed as the lpPassword parameter.