I assume you're referring to David Legland's toolbox from the FEX. It isn't a question of how the term is used "in matlab", it's a question of how David Legland is using it in his toolbox. The best way to get clarification would be to ask him - you could try contacting via his author page, if you haven't already done so.
However, from the documentation for lines2d and edges2d, it seems clear that "line" is used to mean an unbounded line (i.e. without end points), whilst "edge" is used to mean a bounded line, often called a line segment (i.e. with end points).
