Tesla
Tesla is the last name of Nikola Tesla, the greatest mad scientist of all time. Seriously, the dude hardly slept and never had a partner because he was too busy being awesome. It's not like he couldn't pull either, he was considered super handsome in his time.
He is probably most famous for his impressive feats of electromagnetism, up to and including Alternating Current that allowed for long-distance power transmission and making electricity so cheap that even the modern poor can't survive without it, and more iconically the Tesla Coils that shoot lightning which is just fuckawesome. For his contributions to the field, a unit of magnetic flux density was named after him. His apocryphal and alleged inventions have also captured popular imagination, like his earth-resonator and death ray, to the point that the FBI had all his notes and property impounded after his death and called in an MIT professor to sift through it. Sadly, the search turned up nothing, but lots of science fiction has been set in alternate universes where Tesla was really onto something, resulting in an aesthetic heavily focused on Tesla coils, spark gaps, and exposed lightning. Such settings (and some settings set in the distant future) slap the word "tesla" on a lot of their technologies, especially the ones that shoot lightning -- tesla guns, tesla engines, tesla reactors, beans tesla-style, you name it. In this respect, it is very similar to the term "gauss".
When used as a name, "Tesla" is capitalized. When used as a unit or adjective, "tesla" is usually lowercase (though the abbreviation for the SI unit is a capital "T").
Warhammer 40,000
For the fifth edition Codex: Necrons, Games Workshop decided that the Necrons' iconic weapon, the gauss flayer (and its bigger brothers, the blaster, cannon, heavy cannon, and flux arc), needed some nerfing. Being able to automatically wound any infantry target on a six and automatically deal a glancing hit to a vehicle on a six was too much. If the Necron rule development team knew that 6th edition would include "hull points" that would cause vehicles to be wrecked after a certain number of hits (regardless of the results of rolls on the damage table), that was probably also a factor. The gauss rule's auto-glance property was retained, and the anti-light infantry effectiveness was moved to the Necrons' new tesla weapons, horde-killing assault guns that fire off high-strength bolts of lightning that ground themselves on the enemy. Their gimmick is that each to-hit roll of six grants two additional automatic hits on the same unit. Like Gauss weapons only kinda insta-gib vehicles, these weapons only sometimes insta-gib infantry. It does however make Snap Firing (like at Flyers or from Stunned vehicles) a right pain for your enemy, doubly so if the weapon is twin-linked.
- Tesla carbine: A unit of Immortals or Tomb Blades can choose to use tesla carbines instead of gauss blasters, sacrificing the Gauss rule and 4+ armor-piercing ability for the chance to land extra hits.
- Tesla cannon: A tesla cannon is like a tesla carbine with another point of strength and twice as many shots. Annihilation Barges and Catacomb Command Barges mount one slung underneath the operators' pedals.
- Tesla destructor: Again, another point of strength and twice as many shots compared to the tesla cannon. The Annihilation Barge, Night Scythe, and Doom Scythe all mount a twin-linked set of them for vaporizing infantry blobs. The tesla destructor's bolts are so powerful that they can arc extremely far from their initial targets; any unit within 6" of a unit attacked by a tesla destructor gets hit by d6 Strength 5 AP- hits on a roll of six.