A citation analysis is a map of articles in relationship to one another - think in terms of bibliographies graphically depicted. In the picture above, the middle box tagged "Catalan, RG" represents the article: Catalán, Raquel G., José Garay, and Ricardo López-Ruiz. "Features of the extension of a statistical measure of complexity to continuous systems." Physical Review E 66, no. 1 (2002): 011102.
The boxes connecting from the left of the main box represent all of the articles that Catalan et al used to support their research (backward citation analysis). The boxes connecting from the right represent the articles that use the Catalan article to support their research (forward citation analysis). When an article is groundbreaking or the first to present an entirely new idea/research, it is called a seminal article.
Students generally want to find seminal articles when conducting research. They are considered the "primary sources" of scientific literature.
Clouser, Chris. Scientific Information Cycle. Digital image.Searching the Scientific Literature: Scientific Literature. Indiana University of Pennsylvania, 2 Sept. 2015. <http://libraryguides.lib.iup.edu/c.php?g=60424&p=6704019>.