The macrogame refers to the portion of the game spent trying to control the map itself. Let's say you just won a teamfight and aced the enemy team. Everyone backs right away. This was a failure as far as the macrogame is concerned. The correct thing to do would be to take as many objectives as possible. Dragon, towers, Baron if you're not too low. Clear the enemy jungle, you have no idea how much that can screw the enemy team when the jungler doesn't have gold to rely on when he respawns.
It can also involve coordinated dives, like the ones you see in pro play. Someone notices that the enemy ADC is half health and not basing, and that the wave is pushing in your favor and calls for a dive. 3 people go down there and dive his ass.
Micro as opposed to macro is all about your own ability to control your character well. If you've ever watched competitive Broodwar, a lot of the times you'll hear the commentators get excited when after sending one single unit to harass (usually a worker in the early game), he avoids the retaliatory units by microing the worker and wasting precious mental bandwidth for the other player. That's mirco.
So basically, getting outmacroed means they just played to the map better than you did
