Wexis is a humorous term used to refer to the two academic publishing conglomerates which dominate the legal information services industry, namely Westlaw and LexisNexis.
Neither of these companies is independent—they are parts of much larger conglomerates which dominate the entire information services sector. Westlaw is owned by The Thomson Corporation, while LexisNexis is a division of Reed Elsevier.
The Federal Trade Commission keeps a cautious eye on both companies to ensure neither violates antitrust law. For example, both of them are usually required to license the pagination in their printed reporters to the other's online database. Otherwise, lawyers in jurisdictions that require citations to all official and unofficial reporters would have to subscribe to both online services to get all the necessary page numbers for citations in their briefs.
Wexis is a portmanteau.