Terminology!

Common Nerf Terminology

GENERIC TERMS


Aftermarket - Third party, outside-sourced items.
BNIB - Brand New In Box (Never opened, never removed from the box).
CS - Clip System, Nerf ammo system referring to magazine-fed Streamline darts.
EBF - Electronic Belf Fed, unique to the Vulcan EBF-25.
ECS - Electronic Clip System, an battery-operated upgrade to the CS. 
EX - External (I think), blasters which are front-loaded like muskets.
FBO - Full Battle Order meaning (but not restricted to) Head Gear (Helmet, Mask, etc), BDU, Vest, Elbow/Knee Guards, Combat Boots, Gloves, Main Weapon, Side Weapon. [Fish, 190810]
MIB - Mint in Box (Opened but not removed from the box). [Fish, 190810]
Melee - Close range Hand-to-hand combat usually with weapons that are not of shooting capability. ie: swords, daggers, axes. [Fish, 190810]
Mod - Any modification or change done to a stock gun in terms of performance or aesthetics. It generally means upgrading of the blaster's internals to boost performance.
Stock - Any blaster with NO change done to it, not even a new coat of paint.
REV - Revolving barrel, referring to blasters using the auto-advancing barrel mechanism, i.e. Maverick REV-6, Spectre REV-5 etc.
RV - Revolving, similar to the REV but electrically powered and unique to the Barricade RV-10.
SNAP - Simplified Nerf Armament Prototype. Essentially homemade Nerf blasters running on known methods of propulsion (spring, airtank, etc) to propel foam darts. 
Snapbow - the above fitted with a stock for added stability during operation. 

BLASTERS

+Bow/Crossbow - The Nerf Crossbow, both homemade and otherwise.
BBBB - The Buzz Bee Big Blast, usually used to refer to Singled ones capable of accepting darts instead of the regular missiles.
BBx - The Barrel Break IX-2.
DB - The Buzz Bee Double Shot.
Doomsayer/Doomy (and all its variants) - A heavily modded ERTL Rapid Fire Shot Gun (RFSG).
Handcannon - A heavily modded Lanard Sawn Off Shotgun.
Maggy/MS - The Magstrike AS-10.
LAHB - Lego Atlantis Harpoon Blaster. Essentially a reshelled, recolored version of the 2010 version of the Buzz Bee Big Blast with the lever trigger. 
LS - The Longshot CS-6.
LSTK or LSK - The Longstrike CS-6. [Fish, 190810]
LSFG - Longshot Front Gun, the secondary gun of the Longshot CS-6 set.
PAS - The Pump Action Shotgun, or more accurately a heavily modded ERTL Outdoor Sportsman Gun.
RFSG
- ERTL Rapid Fire Shot Gun.

LnL - Nerf Lock n' Load
SSPB - Secret Strike Pocket Blaster



FOAM DART TYPES


CSD - Converted SDL Darts, with tips trimmed and modified to fit N-Strike clips and blasters.
FBR - Foam Backer Rod, a construction/building material that modders use to make DIY foam darts.
FDL - "Fer De Lance" darts, factory manufactured darts designed from R&D by SixShot. Performs more accurately out of the pack than stock darts.
HAX Streams - modified Nerf Streamline darts with the rubber tips replaced with a #4 hex nut secured with copious amounts of hot glue.
OSOK - Converted Nerf Sucker Tip Darts, with tips trimmed and modified to fit N-Strike clips and blasters.
Sabot - Foam darts using rubber sticks (i.e. eraser sticks) as tip weights.
Stefan/Stephy - DIY foam darts created with foam backer rod (FBR) with tips weighted using a variety of materials, ie. hot glue, felt tips etc. Most blasters require further modding to accept Stefans. Usage in Nerf games depend on game organisers rules.
Stock - Refers to Streamlines, Sonics, Taggers and Suction darts sold in mainstream stores with no modifications done to them.

MODIFICATION TERMS


AR - Air Restrictor, the original component that limits air flow to cushion plunger impacts. Typically the first components that are usually removed during a modification.
Barrel - Tube-shaped structure found on the front of the blaster to guide the darts' path. Usually changed to fitting tube material for a stronger air-tight seal.
Bolt - Tube-like mechanism in a blaster which usually chambers the foam dart and is linked to the Plunger tube.
Breech - A foam dart chambering system used in high-level mods to ensure a secure, air-tight seal.
Brass Breech - Originally developed by Forsakenangel24 from NerfHaven, it is a method of creating an air-tight seal in a blaster (commonly the Longshot) from the plunger all the way to the barrel. Higher dart velocity and greater range are usually the end results of such a mod, and the mod is normally performed by modders who have advanced experience in blaster modification. The system utilizes a series of brass tubes cut to specific lengths and accurate measurements/sizing, held together by strong adhesives and installed into the blaster in place of its original firing and chambering mechanisms. 
Catch - A piece in the gun mechanism that holds tension from the spring prior to firing. Usually spring-loaded.
Coupler - Component used to connect an external barrel to the muzzle of a modded blaster.
Dart Post/Peg - Stick-like structure found on ARs that are used to secure darts. 
Dead space - Empty space in the blaster barrel, bolt or plunger that creates inefficient air compression, which reduces performance.
Direct Plunger - Air-delivery system found in certain blasters. Blasters installed with a direct plunger would be able to achieve further ranges and faster dart velocity after modifications than their reverse plunger counterparts due to their efficient compression of air as well as having the appropriate space to accept more powerful aftermarket springs. Guns with larger direct plungers have the highest modding potential, ie. Longshot CS-6, ERTL Rapid Fire Shot Gun & Pump Action Shot Gun, Stampede ECS etc.
Epoxy - Polyepoxide, a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". In essence... very strong glue.
E-Tape - Electrical tape, or black tape, the stuff modders use to secure air-holes, amongst other uses.
PETG - Polyethylene terephthalate tubes, just know that its a suitable barrel replacement material.
PVC - Polyvinyl chloride pipes, material used for wide range of purposes, as structures, barrels or to cover pre-existing modifications.
Reverse Plunger - Air-delivery system found in most modern blasters. Blasters with such a system usually offer less performance improvements after modifications than blasters with the Direct Plunger system (see below), as the space for air-compression is more limited, along with the limitation in fit and choice of stronger aftermarket springs. E.g. Recon CS-6, Raider CS-35, Spectre REV-5.
Singled - Blasters modded with only one single barrel to fire off "single" rounds, usually to devastating effect when used in air-tank based blasters. (Ex. Singled Titan)
Spring - Generally used to refer to a spring-powered blaster's primary means of dart propulsion: the main spring. Modders usually replace the stock springs with stronger ones for more power and distance.



FORUM TERMS


NIC - Abbreviation for "Nerf Internet Community"
WTB - Abbreviation for "Want to buy"
WTS - Abbreviation for "Want to sell"
WTT - Abbreviation for "Want to trade"
Necro - When someone posts in an old topic.  Very frowned upon.
Coc - Short for "Code of Conduct", the general rules of a forum.  Every forum has one.  Newcomers are usually required to read it before posting.


Credit goes to Spartan of the NerfSG forums.  Most of this guide is based off of his. 
If you wish to add something, email me at nerfpause@gmail.com