I can't pull up the link--it works, but I am in China at the moment and we don't have access to Wikipedia or Wiki. If you are looking at vowels, then the term advanced is most likely in reference to tongue root, ATR.
Advanced tongue root refers to the features of a sound made by drawing the root of the tongue forward. This feature distinguishes between tense vowels as [+ ATR] and lax vowels as [- ATR] (Burquest and Payne 1993 18 ). Source: What is advanced tongue root?
You can read more here: (I, however, can't. ) Advanced tongue root - Wikipedia, the free encyclopedia
Does that help?
Retired English Teacher