Somacula, for the evil Soma in the bad ending of either Sorrow game.
"Whip Guy" and "Spear Dude" for the protagonists of Bloodlines.
For Simon's walk in Haunted Castle, "Wedgie Walk" or "Gotta Pee Now Step" apply.
Eeguh - Koji "IGA" Igarashi, the current producer of the series.
Japan refers to Chronicles Simon as either Red Simon (akai Shimon) or... Homon.
Castlevania 64 - The first Nintendo 64 game, properly named Castlevania, starring Reinhardt and Carrie.
The Belmont Walk; the Pimp Walk - A peculiar stride that all of the members of the vampire hunter clan Belmont use. This most likely originated from the four frames of animation use for Simon's walk from the original game, but other 2D Belmonts used it too, leading to the nickname.
Castlevanians of Ottawa-region like to call it "CastlevaNote".
The Samuel L. Jackson Attack - Shanoa's Nitesco + Weapon Glyph union from Order of Ecclesia that resembles a giant purple lightsaber, just like Master Windu's weapon of choice in Star Wars.
Holy Snorkel - The Holy Symbol relic from Symphony of the Night, which allows Alucard to survive underwater and happens to resemble a gold snorkel.
Fleaman - Originally called Hunchbacks, people started calling them Fleamen because of their erratic jumping, and the name kinda stuck, to the point that it's the official name in-game for them.
IGAvanias - For all the Castlevania games produced by Koji Igarashi, almost all of which were "Metroidvanias".
Classicvanias - For all the classic stage-based Castlevania games prior to Symphony of the Night.
Metroidvania - For the post-Symphony of the Night installments in the series for their sprawling world map and wide open exploration. It has also become a nickname for an entire sub-genre of 2D action games offering similar mechanics (for better or worse)
3Dvanias - For all the 3D-based games in the series.
Wall Meat, for the mysterious healing items (usually some sort of roast) that drop when walls are whipped.
Recent continuity has Alucard voiced by Yuri Lowenthal. Japanese-wise, he was at first voiced by Ryōtarō Okiayu, but recent continuity had Mamoru Miyano to voice him (to match Yuri Lowenthal's "youngster" voice?), although Okiayu has returned to the role as of Harmony of Despair.
Signature Scene: The staircase climb to Dracula's room. It's one of the most iconic locales of the series, and whenever the game takes place at Dracula's castle (or a copy of it in Dawn of Sorrow's case), there's a good chance you'll eventually run into that outside staircase with the crescent moon and clock tower in the background.