Hidden city ticketing
Basically means buying a ticket A>M>Z where that is cheaper than A>M, but only going as far as M. Only works on singles (because the return would automatically be cancelled if the full booked route is not flown) and even so might not work after a few attempts (ie once the airline gets wind of the attempt to violate its rules, which do not allow this).
Finding a hidden city route that indeed saves money generally requires many repeated airfare searches for many different destinations on an airline's web site.
For a weekly commute, the column in the middle represents four ‘conventional’ tickets outbound to destination on Mondays and each returning ‘home’ on a Friday – none spans a Saturday so could be more expensive than otherwise:
On the right is one ‘conventional’ ticket but with the return one month later. However the commuter is not stuck at the destination meanwhile, since from there three weekly tickets ‘destination/home’ (the directions are reversed) should get the commuter to the right place at the right time, with each of the three spanning a Saturday and hence perhaps less expensive than otherwise.
One month is only for this example, such commuting may last years at a time. The usefulness of this strategy has diminished materially, as most airlines have abandoned the discount for a Saturday-night stay-over.