Struggling with the distinction between structuralism and post-structuralism? How is a metaphor different from a simile? Dictionaries of literary terms are invaluable for concise explanations of the specialized language of literary scholarship.
A Glossary of Literary Terms by 
A Multicultural Dictionary of Literary Terms by Specialized scholarly encyclopedias are useful for acquiring basic background information on a topic and are valuable places to start your research. Unlike Wikipedia, these encyclopedias are written, reviewed, and edited by academic experts. Consulting an encyclopedia in the early stages of your research can help you define your key terms, situate your topic in its wider scholarly context, find related fields of inquiry, and even locate important works of research that may be contained in the bibliographies at the end of each entry. What follows is a list of general literary encyclopedias and bibliographies—but be sure to sure the library catalogue for more specific encyclopedias by period (e.g. Modernist), geography (e.g. Canadian literature), genre (e.g. science fiction), form (e.g. the novel) or even by major author (e.g. James Joyce).
Oxford Reference Online: Literature by 
The Johns Hopkins Guide to Literary Theory and CriticismLiterature Resource Center
Encyclopedia of World Literature in the 20th Century by Routledge Encyclopedia of Modernism by 
Oxford Bibliographies - Victorian Literature by 
Oxford Bibliographies - American Literature by 
Oxford Bibliographies - British and Irish Literature by 
Oxford English DictionaryLanguage dictionaries give brief definitions of unfamiliar words, phrases, and acronyms.
The Oxford Dictionary of Word Histories by 
The Oxford Dictionary of Phrase, Saying, and Quotation by