Any game that is not a competitive match is a friendly. The main point of friendlies is to maximise training although your economy will also benefit from the "small" amount of money that are made. A popular thing to do in friendly matches is flag chasing, where you visit a new country every week.
For clubs of the lowest division in large leagues (e.g. Netherlands, Spain, Sweden or Germany) are international friendlies (away) not recommendable. The travelling costs will be higher as the spectator income of the match. That teams should make friendly matches against higher division teams of the own country or international friendlies in their own stadions. The economic effect is here also important.
example (german XI. division team):
spectators in series games:
Spectators in a friendly against a IV. division team: