Infusion

An Infusion is a beneficial spell that a mage must maintain in order to keep it active. After you cast an Infusion spell, each round thereafter on your turn you must use the Sustain action to maintain it. If you do not, the Infusion ends on all targets it was cast on at the end of your turn.

The Infusion Focus Keystone ability allows you to use the Sustain action as a Free Action once per round on your turn to maintain an Infusion.

You must use the Sustain action once per Infusion in order to maintain more than one Infusion, though the Infusion Focus Keystone ability allows you to get around this limitation and use a single Sustain action to maintain multiple Infusions.