The phrase "old textbooks" refers to books that are no longer new or up-to-date, usually used in education but can also be used in general. Full definition
In the case of older textbooks or very specialized materials, there may be no financial incentive for publishers to offer materials in both electronic and print format. (slaw.ca)
If it's facts & figures, formulas & ratios, any dry old textbook (which probably has little else to recommend it) will provide them, usually to great excess. (wexboy.wordpress.com)
In the math classroom, you can use scannable tech to update old textbooks. (edutopia.org)