Reviews
Not to be confused with "literature reviews" or "review articles," which are a type of journal article and should be cited as such.

What they are: Short evaluations of other people's works. For example...

• A movie review is an evaluation of a movie.
• A book review is an evaluation of a book.
• An art exhibition review is an evaluation of an art exhibition.

What they give you: The reviewer's opinion about the reviewed work.

Note: In most cases, you should not cite a review. Instead, you should find the reviewed item, and cite that. However, reviews can be useful as primary sources if you want to learn about the public reaction to something. (For example, how did people react to The Wizard of Oz when it first came out?)

How to spot them: 

• Reviews tend to be short -- anywhere from a couple of paragraphs to a couple of pages.
• Look for the title of the item being reviewed, often accompanied by the word “Review”. (For example, “Review of The Wizard of Oz.”)
• There are two titles: the title of the review and the title of the periodical it was published in. 
• There are no citations, except perhaps a citation of the reviewed work.
• The reviewer expresses his or her opinion about the reviewed work.

What they look like in library search results:

What they look like in electronic databases:
(Note that the review begins with a citation to the book being reviewed.)

What they look like in print: 
(Note that the review begins with a citation to the book being reviewed, and ends with the reviewer's name.)