Search engines rank sites (in part) according to the number of other sites that link to them. Wikipedia is ranked very highly in Google largely because many, many sites link to Wikipedia.
The PageRank algorithm to compute these kinds of rankings was one of Google's early innovations, and was the secret to its initial dominance over the early-2000s search engine market.
The PageRank algorithm to compute these kinds of rankings was one of Google's early innovations, and was the secret to its initial dominance over the early-2000s search engine market.