This article first appeared in Genealogy's Star and we are highlighted some of the article, but to read it hit here
The term "brick wall" as used in the genealogical sense refers to an end-of-line situation where the next generation ancestor or even some other relative cannot be easily found. Of course, this could be the researcher's parent or parents but in most cases, it is one or more of a more distant ancestor or relative. As a side note, I think the term is very inappropriate as it implies that some external force is preventing you from finding a particular person. There is a huge body of writings and videos on the subject of overcoming genealogical brick walls, See "The Ultimate Genealogical Brick Wall Buster" for example.
Lately, with the increased interest in genealogical DNA testing, there are numerous examples of articles, advertisements, and other media mentions about finding the "long lost ancestor." Most of these deal with reunions between members of close biological families, i.e. finding parents or siblings. However, there is an undercurrent of articles about solving complex genealogical mysteries, i.e. brick walls, using DNA tests.