Spamming is an act when one deploys a massive numbers of a particular unit, mainly 10-20 points (Like T-55s), or powerful ones (Helicopters are common).
This action, while sometimes can produce success when the enemy gets confused and overwhelmed, at other times will fail because the enemy will simply stack up its counters (eg. If one spams T-55s/T-72s, the enemy will stack up ATGMs, or if one spams Hinds, the enemy will stack up AA)
In general, it is not advised to spam only a certain unit. If one were to make a push, it should consist a variety of units that can cover each other's weaknesses