Rebalance: A hack that attempts to “balance” the game by making changes only to the gameplay.
Redux: See Reskin.
Reskin: A hack that only attempts to change the graphics of a game and not the core gameplay.
Remaster: See Reskin.
Revamp: See Overhaul. Rarely used to mean Reskin.
Reimagined: See Overhaul.
Randomiser: A hack – or the software used to change a hack – that randomises elements of the game.
PME: Pick My Edit/s. See PMU, but can be broader in minor gameplay changes than simply characters alone.
PMU: Pick My Unit/s. A forum game where one user attempts to lightly modify a game or hack’s original characters and other users submit their characters to replace the originals.
Demake: A remake of a game on hardware older than that game, or in the style of hardware older than that game. See: Bloodborne PSX.
Remake: It is what it says on the tin: remaking a game, almost entirely for newer hardware (though not always, see Yooka-Replaylee) and with the improvements of modern sensibilities. See: Spyro Reignited trilogy.
Port: A version of a game created for a different games console or interface than it was originally developed for. See: Final Fantasy VII for PC.
Reverse Recruitment: A form of Fire Emblem hack where units are recruited backwards, starting with the last normally recruited character and ending with the first.
Weapon Reversal: Hack that “reverses” Fire Emblem’s usual weapon triangle, eg. swords become strong against lances.
Alternate Promotion: It is what it says on the tin – an alternative promotion to an advanced class for a character or characters.
Boss Recruitment: Hack where bosses (as in, the main enemies of chapters) are recruitable and playable.
Fixed Growths, 0% Growths, 100% Growths, 255% Growths: You can infer most of this from reading the wiki’s page on growth rates. Fixed Growths works as it does in Path of Radiance (wherein a character must “build up” points to level a stat as they level up, based on their growth rates), 0% Growths means no stat gains on level up, 100% means every stat gained on level up, and 255% is more than one of every stat gained on level up.
Casual Mode: An alternate official playstyle for Fire Emblem games where permadeath is disabled. Compare Classic Mode, where permadeath is enabled.
Easy Mode: It is what it says on the tin: a mode of playing a game where the difficulty is reduced compared to the intended experience.
Demo: Short for “demonstration”, a short piece of a video game used for proof of concept or advertising.
WIP: Work in Progress. A game or hack currently unfinished but in the process of development.
Engine: The software used to design and/or run a game.
Definitive Edition: An “edition” of a game advertised as “definitive”, as in, a version or remake of a game with multiple enhancements and considered to be a higher standard than its original.
Vanilla: Without any changes to the original.
Overhaul: A hack with multiple large changes to both graphics and gameplay (possibly also story/characters).
Rewrite: A hack that changes canon story or character elements that were present in the original game.
Expansion: A hack that builds on story or character elements from the original game, without outright changing canon material.