These are keywords used in the animal kingdom template.
Theme Terms
Animal Kingdom has customized the display names of keywords and card types. When templates are created, they are created using generic terminology. Your player avatar character is called a "hero" and the characters you place on the board to fight are "units". Animal Kingdom has set the display names of these card types to Kings and Animals as per the theme of this game. However the ids of the card types are still referred to as units and heroes by the program. This allows different games to use the same rules even though they have different themes. You can set display names by going to admin->gameplay and looking at the card types section.
Common Terms
Play
To play a card means to activate it, or in the case of units to place it on the Board.
Invoke
To play a card and trigger all relevant abilities except unit's "Invoke" ability without incurring costs.
Summon
Create a card and bring it into the match. Then invoke it.
Special Keywords
Hidden
This unit may not be attacked or targeted by opponent's effect until it comes out of hidden. Using an ability or attacking makes a Hidden unit come out of Hidden.
Silence
Remove all abilities, alterations or statuses on a unit.
Vanguard
With a Vanguard in play other friendly characters that are not Vanguard may not be targeted by attacks.
Twist
Twists are played on your turn but activated on your opponent's turn.
Overload
Reduce the amount of mana you have the next turn by this.
Rush
May attack the first turn it was played.
Combatant
Cannot attack heroes.
Invoke
When a unit is played the Invoke ability is activated.
Legacy
When a card in play is destroyed, activate the Legacy ability.
Warmed Up
While damaged, this unit gains the stated effect.
Last Life
When destroyed, revive with 1 Health and without Last Life.
Frenzy
This unit may attack twice per turn.
Snipe
When this unit attacks it does not suffer any damage from the attack target.
Shield
The first time this unit takes damage that damage is negated.
Offensive
Activate ability when attacking.
Defensive
Activate ability when attacked.
Repeat
Something happens at the start of every one of your turns.
Synergy
Activate the Synergy effect if you played another card this turn.
Conjure
From a selection of 3 random cards, choose 1 to add to your hand.
Knocked-back
Cannot attack for 1 turn.
Rouse
When your hero uses its activatable ability, activate this.
Power Up
When any card uses its activatable ability, activate this.
Sacrifice
May be played only by sacrificing 1 unit you control.
Elusive
Cannot be targeted by Spell effects.
Dust
May activate this from afterlife by paying the cost and removing this card from play.
Remain
This card stays in play until destroyed.
Upgrade
Choose one of 3 buffs.
Haste
May attack animals the turn it is summoned.
Immune
Cannot be targeted by opponent's effects or be damaged.
Echo (Swarm)
After this card is played, a copy if it is created in your hand. It leaves your hand at the end of your turn.
Gemini
When this card is sent into your hand, You also get a fresh copy of it.
Poison
Whenever this card damages a unit, it destroys it.
Lifesteal
Whenever this card damages a character, it recovers your hero by amount of damage dealt.
Spell Power
Increases damage your events deal.
Defense
Reduces damage taken by this character.