The school of New Criticism was made up of an early 20th-century (mostly) American school of critics who were really, really interested in form (literary structures), especially in poetry. These guys (yes, they were almost all guys) decided that the best way to analyze literature is to pretend that it exists in a vacuum.
The reader's response or the author's intentions? The text's historical time period? Political context? None of that matters, people. The text is a self-referential object that may as well be floating in outer space, waiting for us to analyze it, on its own, without any of our own perspectives or biases gumming up the works.
While their view of literature might have been a teensy bit limited, the New Critics helped bring to the fore close reading, a style of analysis that pays really close attention to the form and structure of texts (in other words, what it says and how it says it). We still use close reading in high schools and colleges to this day. Oh, and at Shmoop, too.