These units are the expert scouts and commandos who gather information, set ambushes, sabotage installations, and so on.
Where your unit has the Infiltrators ability:
Count it as in command while it is within 60 cm of its HQ unit, rather than the usual 30 cm. However, it is still destroyed if it becomes Broken and it is more than 30 cm away from its HQ unit.
You may deploy it up to 30 cm outside of your normal deployment zone for the scenario that you are playing. Or, if it is not deployed at the start of the battle then, in the turn when it arrives, you may add +30 cm to its first move — even if its first move is to disembark from transport vehicles or drop pods.