A tribe is essentially a type of minion. If a minion is a part of a tribe, the tribe name will read underneath the card’s name, where other creatures have the word ‘minion’. Battlepet, Structure, Dervish, Arcanyst, Vespyr, Golem, Mech.
You’ll notice each tribe has a theme. Structures and Battlepets behave in a unique way (stationary with no attack, move and attack on their own). Golems are piles of stats while Arcanysts benefit from spells and effects. Dervish is Vetruvian, Vespyr Vanar, and Mechs involve Mechaz0r.
‘Bond’ is triggered like Opening Gambit, with two differences.
Firstly, it only activates if you have a minion of the same tribe already on the board. So Sparrowhawk’s Bond will only trigger if you have an Arcanyst already on board.
Secondly, it triggers when summoned no matter what. What does this mean? Well, Opening Gambit only triggers when the minion is summoned from your action bar. If some effect resummons the minion later, the Opening Gambit does not trigger, but Bond will. For example, if you Keeper of the Vale your dead Sparrowhawk back to life (and you have an Arcanyst on board) it’s Bond will trigger once again.
Hope this helped 