Resilience is a Resistance perk featured in Call of Duty: Ghosts. It is unlocked at level 5 in Multiplayer.
Overall, Resilience is simply a nice bonus to any class. Costing only one point, it is a good way to fill one's class if a single slot is open and is not needed for anything else. However, on some class builds, Resilience can give the player some tactical advantage. The perk can be useful when using Sniper Rifles, as with these weapons it is best to look for high vantage points, and Resilience allows quick getaways from windows or rooftops when needed. Rushing classes benefit from this as well, as when paired with Marathon and/or Agility the player can constantly keep moving without the fear of fall damage.
In Hardcore modes Resilience is even more effective, as the reduced player health means that non-lethal falls in Core can be lethal in Hardcore. The perk allows the player to fall from heights they are normally used to in Core without the need to adjust to the lower health.
Resilience does not protect the player from environmental hazards, such as killzones disguised as long drops. For example, it does not save the player from drowning on Flooded, or falling off of the map on Overlord.
A recently discovered detail about the perk suggests that it does not completely negate fall damage, rather all fall damage is only reduced to 1 point of damage per fall. If one has the perk equipped, climbs up a set of stairs and jumps off multiple times in a period of time, after a while when the player stops, they can still hear the hard breathing from health regeneration (in Standard gamemodes); in hardcore mode, multiple jumps will stack the damage and it will remain until death.
In Extinction, Resilience is a passive perk that is enabled by default in the main game mode, negating all fall damage. The user will still grunt and wince when falling from high places, but no fall damage is applied. Resilience is disabled when Fragile is activated. Resilience is also disabled by default in Chaos Mode, and cannot be gained in any way.