|informal (US), (Canadian) a booming or thriving business|
A thriving, expanding, or very profitable concern or volume of trade. For example, After the storm they did a land-office business in snow shovels and rock salt. This term, dating from the 1830s, alludes to the throng of applicants to government land offices through which Western lands were sold. It has been used for other booming business since the mid-1800s.