From WordNet (r) 3.0 (2006) [wn]:
line of business
n 1: a particular kind of product or merchandise; "a nice line
of shoes" [syn: line, product line, line of products,
line of merchandise, business line, line of business]
2: a particular kind of commercial enterprise; "they are
outstanding in their field" [syn: field, {field of
operation}, line of business]