( .\flmaterials.dll ) ???

Nothing. It doesn’t matter. Ignore it and move on.

F!R is right .\ means the directory in which the filepointer (for Example Freelancer\EXE\ is currently.

.\subdirectory\flmaterials.dll

would point to Freelancer\EXE\subdirectory\flmaterials.dll (-> looking from Freelancer\EXE).

…\Data\subdirectory\flmaterials.dll.

…\ would change into the next higher directory (Freelancer in this case) by “…” after it to the Data and after it to subdirectory loading the mentioned dll from this location (-> looking from the Freelancer\EXE again).

This way you are able to place for example the dll’s you want to load into a directory of your choice while keeping the priority directory.

Or said in short - the system is locked in the exe folder and have to be pointed to every single location of files.

Don’t confuse things. The question was: is there a difference between “.\flmaterials.dll” and “flmaterials.dll” and the answer is that there isn’t. “…” is another thing entirely.