Terminology

Numeral Duplicated URLs
If you have different pages with same titles and want to use both of them (not to set which one to be active and other inactive) then you should set to YES this option in AceSEF configuration or extensions parameters.

Record Duplicated URLs
If set to Yes, Real URLs that yield the same SEF URL will be recorded. This will allow you to choose which one you prefer, assigning it as "Used".

non-SEF Variables
Variables that will be removed from SEF URL and appended behind. This feature excludes often changing variables from SEF URL and appends them as non-SEF query and will decrease database usage and also prevent duplicate URLs in some extensions. Enter each variable separated by comma and space like: catid, view=article.

disable-SEF Variables
Variables that will prevent creation of SEF URLs in case of they are included in Real URL. This feature is usefull expecially with components that uses AJAX, Captcha etc. functions that have to not being SEF'ed. Enter each variable separated by comma and space like: catid, view=article.

Skip-menu Variables
Variables that will prevent prepending menu title to SEF URLs in case of they are included in Real URL. Enter each variable separated by comma and space like: catid, view=article.

Router
Defines how will AceSEF rewrite URLs.

Used
This term is used for duplicated URLs. Used URL means active URL for duplicated URLs. In the Used column one of the URLs has a solid star and others have a hollow star. The solid star means that this Real URL will be used for this SEF URL.

Locked
The long term is Delete Locked. If you have URLs that have good ranking and dont want to lose them then you can LOCK them to prevent any deletion for accident.

Blocked
The long term is Block Rewrite which means that if you want the URLs to be used as Real (default Joomla!) URL not SEF then you can BLOCK it.

Red URLs
The long term is not-handled "Duplicated URLs" which means that if you have some duplicated links and you did nothing to fix them, like setting one as Used or changing the SEF URL or anything else, all these links will be in red color, like saying pay attention.