Something that is selling rapidly and well (Salespersons) (1930s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with hot number
hot stuff. Someone or something that is currently popular or fashionable; also, someone or something unconventional or daring. For example, That new song is going to be a hot number, or He really thinks he's hot stuff. These slangy expressions use hot in the sense of “recent” or “fresh,” a usage dating from the 1300s, although hot stuff dates from the 1700s and hot number from about 1900.