In other words, if a school's 25-75% LSAT numbers for it's 2005 entering class were 158-162, this means that a quarter of that school's 2005 entering class had LSAT scores below 158, a quarter of them had LSAT scores above 162, and the remaining students had scores that fell somewhere in between 158 and 162...
When used in conjunction with the school's 25-75% GPA numbers, these stats help applicants gauge their chances at a particular school...for example, if your GPA falls below the 25% number of a certain school's GPA range, then your LSAT score would probbaly have to be above that schools 75% number of their LSAT range in order for you to have a realistic shot at admissions...