Why "line of business" applications?

A company's line of business is a more generic term for what would be known as a product line or product line-up in a manufacturing or retail business. This itself comes from the days when a typical retailer had only a roadside still, with wares lined up in front of him.

This is also where we get the terms sideline and top of the line from.

Line of Business Applications, like many IT buzzwords, has drifted a little from it's literal meaning. It's most frequently use for those applications which are those most critical to the running of the main business of the company, but also for those which are unique, bespoke or specific to that business or industry too (as opposed to say email software or web servers).

Line of business has a number of meanings, but in computing it refers to any of a set of critical applications for running an enterprise.