Spamming is when you build up alot of one unit for example maus's and then after you have alot you charge at the enemy. A huge spamming of Maus's is really hard to defend against. One tip I have if you are in this sort of situation is to stop the bluck of the army with aircraft (They may not have anti-air if they are doing an all tank spam). Then at your base have a ton of at guns and a recon hidden in a forest and bombard the rest of them. Then you make sure any means of production for them is gone. When they are probably max (xbox only allows a certain of units and buildings) You can send paratroppers at their base. Maus's aren't fast enough to counter this so you have both sides against them and it will be hard/impossible to rebuild.
In R.U.S.E spamming is highly frowned upon and is not like amongst players. R.U.S.E is about tactics. Not having the idea to spam about 40 Maus's at them.