Every hunter pet family is linked to one of three specializations ('specs') - Cunning, Ferocity, or Tenacity. Your pet's specialization cannot be changed, unlike the changeable spec system of Legion. For a discussion of the old spec system see this page.
Each spec is distinguished by the two abilities it grants (see the table, below). One ability is a passive that operates constantly, and the other is an on-use spell, with a cooldown.
All specs should be viable for solo play - so pick whichever pet makes you the happiest or suits your play style! In dungeons and raids you may need to pick a pet with abilities that suit your group. Note that in previous expansions Tenacity was synonymous with tanking, but this is no longer strictly the case.
|"Guileful creatures capable of skillfully mitigating lethal blows dealt to themselves and their allies."
|"Driven by a frenzied persistence to pursue prey, these beasts stop at nothing to achieve victory; even death is temporary for these predators."
|"Stalwart and veteran defenders who unquestionably place their thick hides and protective exteriors in harm's way for their allies."