List of BMD Terms used in Weapon Modification Descriptions

Firemode
Also known as: Automatic, Semi-automatic
This denotes how a weapon operates and will only be listed if it can be
changed via mods. For example, the 10mm Pistol Receivers list their fire
mode, as it can made either automatic or semi-automatic, but the
Hunting Rifle Receivers do not, as it's always bolt-action.
Simple: Automatic = May benefit from Commando Perk. Hold Fire to keep firing.
Semi-automatic = May benefit from Rifleman Perk. Repeatedly click to
fire.
Not listed if only a single firemode is available to the weapon.

Weapon Type
Also known as: Pistol, Rifle
Usually found listed on stocks/grips, this shows what kind of weapon the mod
will make. Laser weapons, for example, are laser pistols if equipped
with grips but laser rifles if equipped with stocks. If a weapon cannot
be modified to another type, this info is omitted.
Simple: Rifle = May benefit from Rifleman Perk. Usually has a stock and is more
accurate while aiming. Pistol = May benefit from Gunslinger Perk.
Usually has a grip and is more accurate while hipfiring.

Damage
Also known as: Bash Damage, Bleed Damage, Burn Damage, Poison Damage, Critical Damage, Sneak Damage
This denotes the damage dealt. Usually will come in the form of '+25%
Damage' and denotes exactly how much more (or less) damage a weapon will
deal.
In the case of Plasma weapons, this includes both ballistic and energy damage.
Bash Damage refers to the damage a gun deals when being used in melee.
Some damage types are dealt over time. These are Bleed (over 5 seconds), Burn (over 3 seconds) and Poison (over 10 seconds).
Critical Damage is the damage dealt by Critical Strikes (in VATS). Sneak Attacks are not increased by this value.
Sneak Damage is the amount by which the Sneak Attack multiplier is increased.
Simple: More Damage = better (makes stuff deader). Less Damage = worse (makes stuff not as dead).

Mag Size
Previously known as: Ammo Capacity
Mag Size is very straightforward: How much a weapon's magazine is increased
(or decreased) by a mod, based off its base value (usually with the
standard magazine equipped). Larger Mag Sizes mean a gun can fire more
rounds before needing to be reloaded.
Simple: More Mag Size = better (bigger). Less Mag Size = worse (smaller).

Reload Time
Previously known as: Reload Speed
Reload Time denotes how long it takes to reload a gun. Less Reload Time means
it takes less time to complete a reload. Usually larger magazines have
longer reload times.
Simple: Less Reload Time = better (faster). More Reload Time = worse (slower).

Fire Rate
How fast a weapon fires. Note that the weapon info menu in the game lists
fire rate as the amount of shots a weapon can fire in 10 seconds and
displays rounded values.
Simple: More Fire Rate = better (faster). Less Fire Rate = worse (slower).

Range
Also known as: Min Range, Max Range, Damage At Max Range, Reach
Range determines how far a projectile can travel and still deal maximum
damage (Min Range). Once it passes this mark, it will lose damage in a
linear fashion until it hits Max Range, at which range and beyond it
will only deal 50% damage (unless modified by Damage at Max Range). Some
weapons have a very limited range (e.g. Flamer) and seems to be
governed by different rules than normal projectiles. In this case range
is referred to as reach to differentiate (with Reach being the maximum
distance out to which the weapon can deal any damage at all).
Note that Range values are usually given in '10x Min Range' or '18x Max
Range' format and denote how much they affect their respective distance.
I'm afraid I don't know that measurement these ranges are in and thus
can't give any comparison.
Simple: More Range = better (less damage loss at range). Less Range = worse (more damage loss at range).

Spread
Other terms: Sight Spread, Min Spread, Max Spread, Spread Increase Per Shot
Previously known as: Accuracy, Hip-fire Accuracy, Sighted Accuracy, Accuracy Penatly While Firing
Spread is the amount by which any shot you fire will possibly stray off
center. The higher the spread, the further it might deviate, making a
weapon less accurate. Conversely, a highly accurate weapon has very
little spread. Weapons are generally also more accurate when aiming down
sights (referred to as Sight Spread, which is based off Min Spread and Max Spread below) and not being hipfired (firing while not using a sight).
Min Spread is the minimum amount by which a shot will go astray when firing
from the hip. Max Spread is the maximum amount by which a shot will go
astray when firing from the hip whilst moving. Spread is both of these
combined (usually when a mod increases or decreases both values by the
same amount).
If one keeps firing continiously, spread starts building up (up to Max Spread). How much it does so is governed by the
Spread Increase Per Shot, which is only modifed by a single attachement
(Long Finned Barrels for Pipe Weapons).
Simple: Less Spread = better (more accurate). More Spread = worse (less accurate). Sighted Spread = while using sights. Hipfire = firing whilst not using sights.
Spread Increase Per Shot = Weapons become less accurate if fired
continuously instead of in short burst.

Sight Sway
Previously known as: Better aim with scopes
Sight Sway modifies how much a sight randomly moves around when the user
isn't holding their breath. Low zoom optics seem to be unaffected by
sight sway. Less sight sway means the scope will move around less.
Simple: Less Sight Sway = better (less scope movement). More Sight Sway = worse
(more scope movement). Sight Sway can be temporarily reduced by holding
breath whilst scoped in.

Sight Time
Sight Time refers to the time it takes to bring a weapon's sight up fully from the
resting/hipfire position. Longer barrels and stocks usually increase
this time whilst lighter versions usually decrease it. A lower Sight
Time is preferrable.
Simple: Less Sight Time = better (faster aiming). More Sight Time = worse (slower aiming).

Recoil
Also known as: Horizontal Recoil
Previously known as: Per-Shot Recoil
Recoil is the amount by which your weapon physically moves up or to the side
with every shot. This is distinct from spread as a weapon might have low
recoil but high spread, meaning the user won't actually see any
movement of the weapon but the shots will go wild. Converesely, low
spread but high recoil would also be inaccurate beyond the first shot as
the recoil would throw the user's aim off but could be countered by
moving the mouse.
One odd case is the Compensator Muzzle Modification: it reduces Horizontal Recoil by 100%, something the more
advanced Muzzle Brake or Suppressor mods don't do.
Simple: Less Recoil = better (weapon jumps around less). More Recoil = worse (weapon jumps around a lot).

Other
Armor Pierce: A percentage of enemy armor is ignored, causing more damage to be dealt.
Disarm Chance: Target may drop their weapon.
Night vision: Scope has a green tint and makes it easier to see at night.
Stun Chance: Target may be briefly stunned.
Suppressed: Suppressor installed. Weapon sound reduced, harder to detect for enemies and benefits from Sandman Perk.
Tracks target: Recon Scope tags a target with a red diamond over their head.
Uses X Rounds: A receiver mod causes the weapon to use a different kind of ammunition (X = .308, .38, .45 or .50).
Zoom: The amount by which a sight zooms. Ranges from 1x (Standard Sights) to 10x (Long Scopes).