Definition: Top and bottom coding
It consists in setting top-codes or bottom-codes on quantitative variables. A top-code for a variable is an upper limit on all published values of that variable. Any value greater than this upper limit is replaced by the upper limit or is not published on the microdata file at all. Similarly, a bottom-code is a lower limit on all published values for a variable. Different limits may be used for different quantitative variables, or for different subpopulations.
ESSNet SDC (Network of Excellence in the European Statistical System in the field of Statistical Disclosure Control), under the coordination of Anco HUNDEPOOL, "Handbook on Statistical Disclosure Control", version 1.2 (2010 Edition)