Wiktionary
line function
n. (context: management) Any primary business function that would affect customers or profits if interrupted
WordNet
line function
n. activity contributing directly to the output of an organization [syn: line duty]
Wikipedia
Line function
In management, a line function is any kind of daily operation such as purchasing, manufacturing, and selling that is directly involved in carrying out the purpose of an organization. This contrasts to a staff function, which involves the provision of advice and other support to those involved in a line function.