Non Armor Defenses
Non-Armor Defenses, or NADs, is a /tg/ term derived from a game mechanic in Dungeons & Dragons, which became a part of the game with the 3rd edition. (Previously, we had Saving Throws. See below.)
Back in Advanced Dungeons & Dragons, players had a wide array of class-based (and sometimes race-modified) saving throws they could make against different kinds of threats; these got kind of convoluted, with separate saving throws for both spells cast directly by a caster and for spells cast from a wand, for example. So, when third edition rolled into town, they discarded the extensive list and replaced it with three new defenses; a player just had to roll the appropriate save when it was called for.
Fortitude covers how tough a character is, and thus how well they can resist things like poison or disease.
Will covers their strength of will, which defines how easily they can resist mental attacks.
4th edition changed these by switching them from being a save the player made into static defenses, which is arguably where the name came from; now, Fort, Ref and and Will were player scores the DM had to roll against, like Armor Class, rather than saves the player had to make.
5th edition either expanded on or abandoned NADs entirely, depending on how you look at it, replacing the whole system with a universal "make a saving throw with a bonus/penalty from the relevant ability score" style mechanic.
Star Wars D20 Saga Edition, a spin-off (rules-wise) of a spinoff from D&D, took the unusual step of removing Armor Class and rolling it into Reflex. This carries the oddity of armor making it easier to dodge things, but this matters less than one would think since only NPCs and specialist PCs wear armor in Saga Edition and most of the cases are situational anyways.
13th Age also has a more simplified variant, keeping AC while giving only two NADs with only Physical Defense (measured by the median of your phyiscal stats) and Mental Defense (measured by the median of your mental stats). However, while AC can be influenced by what armor you wear, your NADs are not so easily impacted.
Before 3e, like a lot of things, we had a confusing mess. AD&D's system was known as "Saving Throw against X"; a character's saving throws were as follows:
- Paralyzation, Poison, or Death Magic
- Rod, Staff, or Wand
- Petrification or Polymorph
- Breath Weapon
The first fun thing? This was all governed by a bigass table towards the back of the PHB (also found in the DMG), with no explanation of how it was derived, and had bonuses and penalties that you had to add and subtract yourself.
The second fun thing? Figuring out which saving throw to apply. During the 1st Edition, no explanation was offered, so nobody knew what save to use for a polymorph wand or paralyzing breath weapon. 2nd Edition had an explicit "top down" rule (higher on that list? Higher priority, with a few notable exceptions).
Fun fact: "Saving Throws" originated in Tony Bath's Rules for Medieval Wargames, where attackers made a to-hit roll, and then defenders had a "saving throw" to see if their armor protected them--as every unit in that game was a one-hit-point-wonder, this was the only way of surviving such a hit. Chainmail then chose to include saving throws for Hero units. To provide a bit of the feel of Chainmail's saving throws, the rule for dragon's breath was as follows: "Dragon fire will kill any opponent it touches, except another Dragon, Super Hero, or a Wizard, who is saved on a two dice roll of 7 or better."
Save or Die/Save or Suck
One common complaint in a lot of systems is that conditions tend to be rather fatal or completely debilitating like blindness or losing all non-movement actions. This effects are typically known as "Save or Die", "Save or Lose" and/or "Save or Suck" in order of descending lethality with no clear line of division (aside from spells that do cause outright death clearly being the first name). Among the systems this problem exists in are several editions of Dungeons & Dragons, Exalted, and Call of Cthulhu.
Ultimately the issue isn't in saving throws themselves, but in the ease of obtaining effects that cause them and how they are no easier to make than effects that merely damage.