noun, colloquial, archaic. Back in the olden days - a term which here refers to that period of time between the invention of reliable, relatively cheap photocopying, and the invention of reliable, relatively cheap broadband internet - a student attending a tertiary institution such as a college or university might be required to purchase a reading brick along with their textbooks for each subject. The reading brick consisted of photocopied extracts from various books and journals, and included parts of the required reading and supplementary reading for the subject. Bricks were usually copied onto A4 paper and stapled in blocks about 1cm thick.
The reading brick was gradually superceded by burnable CDs and thumbdrives, which were at least smaller; and these days students are simply given a list of links to downloadable PDFs or electronically accessible journal articles. This is lighter, cheaper and easier. On the other hand, it's very difficult to use a PDF to prop up a wobbly table leg, block the draft through a dodgy window, or hold over your head as an umbrella while running between classes.