Spells with the Cantrip tag can be cast with only 1 Major Action. Some abilities (such as Warlord's Command and Inspiring Strike) interact with Cantrips in different ways than they do with spells that lack this tag.
When you cast a Cantrip as a Free Action or Reaction outside of your turn, it loses the Exceptional tag, but you can only spend at most 1 charge of Mana Flux to add Metamagics to it.