Particles are a graphical effect in Minecraft. Particles always seem to face the player and will usually disappear after a short period of time. They only appear from another entity such as fire. Particles collide with solid blocks and are slowed down by cobwebs, but are unaffected by other entities. Each particle texture is 8x8 pixels.
You can reduce the amount of particles visible in the Options menu. These options range from All to Minimal. All renders all particles, decreased renders half the amount of particles, minimal only renders block breaking particles. As of 14w04b, /particle can be used to spawn particles.
In Minecraft's code one can find a variety of particles. To help coders or curious players, the types of particles and their coding names in the game's code are displayed below.
Particle names in italic will always be shown, even if the "Minimal" particle setting is used.
If you would like to execute this command to make particles, make sure to use this command. Keep in mind that [count] and [player;entity] are optional.
/particle <name> <x> <y> <z> <xd> <yd> <zd> <speed> [count] [player;entity]
Issues
Issues relating to "Particles" are maintained on the bug tracker. Report issues there.
Trivia
Most particle colors can be changed using resource packs, however the color of smoke particles used in redstone, portals, and Endermen can't be changed without mods.
The rain particles affect the rain sound.
Mobs spawned using a Monster Spawner emit smoke particles when spawning.
Particles are slowed when passing through a Cobweb.
Particles will appear where your face is pointing.
Bubble particles seem to only appear when they are in water.
Gallery
This is a picture of the render radius of particles. It seems to be round, but not entirely circular, as seen at the back.
An image of particles.png with the primary purposes of each particle texture explained.