|This article does not cite any references or sources. (February 2012)|
In marketing terminology, a killer feature is any attribute of a product that, for a particular type of use, becomes essential to those users due to its usefulness. The killer feature effectively kills off competitors from the market that needs it.
The word is used mainly about software, analogous to "killer application", the difference being that the latter specifically refers to software as a killer feature of its compatible hardware.