Is Wikipedia an encyclopedia?
In her 2010 PhD thesis, Daniela Pscheida writes constantly about ‘the so-called online encyclopedia Wikipedia’ and ultimately explains why Wikipedia according to her is no encyclopedia. She thinks that Wikipedia misunderstood its own identity:
- On the one hand, Wikipedia sees itself in the tradition of encyclopedias.
- On the other hand, Wikipedia exceeds the limits of the genre encyclopedia by accepting new topics such as contemporary events.
Wikipedia to her is a database. 
Maybe Daniela Pscheida’s opinions relate to the fact that she describes Wikipedia quite well and extensively but (for any reason) did not notice our rule No Original Research. At the end, she even recommends that scholars establish new theories via Wikipedia, aside the traditional way of peer-review.
Whether Wikipedia is an encyclopedia or not, we can argue. About this last thing, we can’t. Sorry.
Modern encyclopedias and our concept of an encyclopedia were shaped in the 18th century. Earlier, the notion and the subject already existed, but were not linked the way we tend to do nowadays. The ancient Greek term is of uncertain etymology. Paul Scalich’s Encyclopaedia of 1539 was the first reference work to have the word in its title. 
Not only are there a lot of expressions for an encyclopedia, the content was very diverse and presented in different ways. Based on that, it is difficult to exclude a work from the list of encyclopedias if it does not match to what somebody has in mind.
An encyclopedia does not cover contemporary events and things? It does, this was the main intention of the original ‘Konversations-Lexika’, to capture the Zeitgeist and help the reader to participate in conversations about society and politics.
Ulrike Spree wrote that people thinking about encyclopedias don’t have a list of criteria in mind, but prototypes. In the prefaces of their works, the authors or publishers file their work in the tradition of encyclopedias, using other encyclopedias as model or as counter-example. Wikipedia is not different.
For example, it seems to be more common in Germany than in the English-speaking world that readers complain about the length of Wikipedia articles. According to them, an encyclopedia consists of rather short articles. This may relate to the fact that in the German-speaking world the most popular traditional encyclopedia was Brockhaus, a short-article-encyclopedia.
In 2005, the German language Wikipedians had a discussion about footnotes, whether to use them in articles. Several of them said that footnotes are not used in an encyclopedia. Again, it depends on the historical model you follow.
In 2007 German Stern magazine presented a close comparison of Brockhaus and Wikipedia, in which Wikipedia appeared to be the better encyclopedia, Klaus Holoch said that the Wikipedia principle is interesting. But Wikipedia is not an encyclopedia (‘Lexikon’), he claimed, because it is gratuitous and unchecked.
Incidentally, Klaus Holoch was the chief sales representative of Brockhaus.
 Daniela Pscheida: Das Wikipedia-Universum. Wie das Internet unsere Wissenskultur verändert. transcript, Bielefeld 2010, pp. 442-446.
 Ulrike Spree: Das Streben nach Wissen. Eine vergleichende Gattungsgeschichte der populären Enzyklopädie in Deutschland und Großbritannien im 19. Jahrhundert, Niemeyer 2000, p. 17/18.