A mine is a kind of defensive weapon used to restrict or block access to an area of space. There are several varieties.
These are usually set up around otherwise vulnerable worlds. Normally inert, they must be activated from a command and control centre during an attack. This is to prevent accidental detonation and navigational hazards. 
These are a type of plasma weapon launched from either a ship or space station towards an advancing enemy and detonate when they reach a certain proximity. G'Quan class heavy cruisers are equipped with energy mine launchers.
A blockade mine is effectively an automated orbital weapons platform that can target and fire on enemy ships. They are dropped by starships and used to secure areas of space or planets to prevent an enemy from escaping or to stop reinforcements from getting through. They do however have their limitations and are easily cleared by even medium warships. They are mostly effective against transports, fighters, and slower vessels. 
Behind the Scenes
|Phased Plasma Guns|
|Auricon PPG Pistol · Westlake & Grummon PPG Pistol · Tho'val PPG pistol · Kalat PPG Pistol · Sha'ann PPG Pistol · Tromo PPG Pistol · Auricon PPG Rifle · Auricon PPG Sniper Rifle · Auricon PPG Assault Rifle · Tromo PPG Rifle · Centauri PPG Rifle|
|Denn'bok · Shock stick · Coutari · K'tok · Barrken · Minbari glove-knife · Drazi Blades · Graal · Electro-whip · Slaver's glove|
|Nano-virus · Drakh plague · Techno-mage nano-virus · Telepath · Morph Gas · Assassination device|
|Weapons of Mass Destruction:|
|Thermonuclear device · Mass driver · Vorlon planetkiller · Death Cloud|
|Energy mine · Perimeter mine · Blockade mine · Planetary defense grid · Slugthrower · Thermal Grenade · Hand-held Grenade Launcher|
|Michael Garibaldi's Smith & Wesson · Marcus Cole's pike · Londo Mollari's coutari · Ta'Lon's k'tok|