Coordinated attack is a feature in Supreme Commander that was highly-touted prior to release.
Basically, to coordinate an attack, you set one attack order with one group of units, select another group of units, and then double click on the same attack point on the map as the first group. The two groups will theoretically coordinate with each other to arrive at the same time, with the group that is nearer (in time) to the objective slowing down or even waiting for the other group to arrive