passives are things which change the way a ship works, but don't have to be triggered by the player. hence why they are passive, as u dont need to do anything for them to do their thing.
ablative hull armour is a passive, all defiants come equipped with it, u dont have to trigger it. it has an icon on the single ship overview. ablative hull armour has 2 effects:
1) damage received from short range attackers (enemy unit being short ranged, not being close when firing) is reduced by 50%, this is a positive thing.
2) the weakness which counter balances the positive is that the hull of the defiant regenerates slower.
this passive is always on, any time something which is short ranged attacks a defiant, it does 50% less damage.
the vorcha pulse turret sovvie and t15 have ablative armour too.
lets analyse another passive called Single Stage Energy Conduits (SSEC)
it has the following effects:
1) any ship with SSEC does 31% more damage to medium ranged opponents.
2) the counterbalance is that ships with SSEC lose subsystems faster.
the kvort breen ships and leahval are famous for SSEC, when they try cloak under fire, they may lose subsystems easily when their hull takes fire. also weapons like the v-13 excessive strike (which deal direct hull damage) will hurt these ships more.
here is the guide page on the damage system, at the bottom are the most common passives:
Damage System - The Hitchhiker's Guide to Fleet Operationsas u can see from reading that, most passives are range based.
also passives have good and bad sides, so ADAI units are great, unless your enemy makes lots of support ships. etc etc.
a lot of vessels have passives. so spams are easily countered.
passives make vessels unique, giving them roles to fulfil.
the borg ability you may be thinking of is for the optimise sphere with prime modules. they passively remove energy from the enemy. u dont have to trigger them.
EDIT: there are other passives not listed in the guide, but these are rare and only appear on 1 ship usually. like the noq duj (klink scout) has the improved tactical overlays (used to be called superiority fighter i think) passive, meaning it can hunt enemy scouts.
