Spencer Lenfield in Harvard Magazine:
“Close reading” was the favored term of the New Critics in the 1930s to describe and denote the method of interpretation they advocated to replace the philological criticism and belletrism then dominating the study of literature. They wanted to study poetry not just as an instance of language, but as art. However, they insisted that literary study should be more like a science than like mere book-reviewing, with a rigorous consideration of a poem as a self-enclosed object possessing its own internal coherence. At its best, close reading is the literary equivalent of microscope work in a biology lab: scrutinizing every element of a poem, no matter how minute, and its impact on the poem’s range of meaning. The technique, which has long outlasted the doctrine that gave it rise, has forcefully shaped the way poetry is taught in the English-speaking world in both high schools and colleges. Entire class sessions are often spent on a handful of short lyric poems. It is somewhat unusual to find a syllabus assigning an entire volume of poetry by a single poet that is taught as a continuous whole rather than as a set of discrete texts.
More here.