We use Tags in two different places/ways:
Clicking on "ap_buff" in the Tags column shows all the Cards tagged ap_buff.
On Units
We use Tags on Units to denote a unit's state of being, or to denote special abilities that a unit has. These are the Tags that we have so far:
Indirect
This unit does not need Line of Fire to Attack a target.
Teleporter
Any unit tagged 'Teleporter' within RG of another friendly unit tagged 'Teleporter' will form a network that units can teleport through.
Spotter
Units with the Spotter Tag do not use Line of Sight (LoS) to determine which squares they see; they simply see every square within their VS. Spotters also remove the Cloaked Tag from enemy units.
The Spotter Tag lets Hartshorne ignore Opaque objects when determining Line of Sight. Hartshorne simply sees everything within its VS.
Cloaked
Units with the 'Cloaked' tag cannot be seen by the enemy. The 'Cloaked' tag can be removed if the 'Cloaked' unit enters a square adjacent to an enemy unit or enters the VS of a unit with the 'Spotter' tag. Because units with the 'Cloaked' tag are considered "not there", they do not block Line of Fire. A unit that is both 'Cloaked' and 'Revealed' cannot be attacked by units, but it can be targeted with cards.
Cloaking
A unit tagged 'Cloaking' has the ability to become 'Cloaked'. A unit tagged Cloaking is not tagged 'Cloaked' when it is first Called onto the battlefield. In order to gain the 'Cloaked' Tag, a 'Cloaking' unit must either Move (to a square not visible by the enemy), or have an Upkeep while not visible by the enemy and while not tagged 'Revealed'.
Opaque
Squares on the Map are translucent by default (units can see through them). Units are also translucent by default. A Unit can be tagged 'Opaque' so that it cannot be seen through. Units and terrain tagged 'Opaque' have an additional property that make them permanently 'Revealed.'
Permeable
Squares on the Map are 'Permeable' (they do not block Line of Fire). By default, units are Impermeable. Example: Unit A cannot shoot Unit B if there is some intervening Unit C blocking your Line of Fire to Unit B. If Unit C is tagged Permeable, it does not block line of fire to unit B.
Revealed
When a unit attacks another unit, both units get the 'Revealed' Tag. A unit tagged 'Revealed' is at a known position and thus remains visible even if the tagged unit is in the Fog of War. To remove the 'Revealed' Tag: move the unit. If you try to Attack a unit and discover an intervening unit in the Fog of War blocking your Line of Fire, the discovered unit is tagged 'Revealed' (this is covered in more detail under Combat).
Captain
Each player starts a match of Just Tactics with only three units on the map, these three units are 'Captains,' a.k.a Squad Leaders. From left to right, your Captains have attached to them all Call Unit Cards from Alfa, Bravo, and Charlie Squads.
Deployable
Deployable units are a classification of units that are not available in the deployment editor. They come attached to other units and therefore do not have a cost. Some of the current deployable units can be found here.
In the Deployment Editor
All Cards have one or more Tags on them. Tags let you browse/sort/search/find Cards in the Deployment Editor. Examples: all Cards that give AP are tagged "ap_buff" and all Unit Call Cards are tagged "units."