A Lexile Measure "scores" the difficulty of text and the reading level of readers. A student gets his or her Lexile measure from a reading test or program. The Lexile measure is a part of the "Lexile Framework for Reading." According the Lexile website,
The Lexile Framework for Reading is a system that can help determine the reading level of any written material—from a book to a test item. The Lexile Framework can also be used to assess a readers' reading comprehension level. After test results are converted into Lexile measures, readers can be matched to reading materials on their own level and comprehension rates of readers can be forecasted to determine how well a reader will comprehend thousands of texts that have been measured in the Lexile metric.