Much like World of Warcraft's launcher, "Playable" means the launcher has downloaded sufficient game code and initial media for you to launch the game and start playing it.
Unlike "available" where you run into "loading walls" where the game client struggles to keep up with downloading media necessary for you to play, "playable" means it has downloaded enough data for you to play without hitting any "loading walls".
Setup (Red): Core game content is being prepared. You cannot enter the game at this time.
Available (Yellow): Major game content is not completely applied. You can play, but your game experience will not be ideal.
Playable (Green): Final game content is almost complete. You may experience a few issues with playing at this stage.
The "Playable" includes high resolution textures and other low priority flair:
Q. How is data assigned to each stage?
A. Data is assigned to each stage based on the relative need for that data. Red is required to get into the game, Yellow is data needed for baseline gameplay, and Green is for variants of base game data (higher-resolution graphics, alternate sounds, other flavor data). [1]
Therefore, "optimal" means it has completed downloading all available content and will not impact your play experience with background downloads.
(Information is from World of Warcraft's launcher, which uses the same technology)
Half-Carries or Semi-Carries are heroes that have the potential to carry the team in mid and lategame but will lose most likely to any "hard" carry.
The difference is the fact that a semi-carry has a better early game (escape mechanism, better farming tools, more teamfight potential for mid-game and overall more flexible[movement and items]) resulting in a much faster scale to late-game.
Examples of semi-carries are:
Mirana (she can dish out a ton of damage but can also gank, solo, farm with spells, etc)Queen of Pain (aoe spells to spam and farm, ganking , solo) simply carries the team till late [when magic dmg isn't relevant anymore] and then pass the role to the real (hard) carry.
compared to hard-carries:
Faceless Void (needs a babysitter, has no teamfight potential until he has his core items, no aoe spells to farm creeps)Spectre (same as void)
Furthermore the hard-carry has a ability that scales incredible well in late game (semi-carry lack these). For example: void - backtrack + time lock; spectre - dispersion + desolate; weaver - geminate attack; morphling - morph + adaptive strike; naix - feast + rage.
Best Answer
I don't have any sources for this other than years of playing, but, for me:
A beat-'em-up is like Streets of Rage or River City Rampage. There may be some items and character progression, but the majority of combat is determined by player reflexes and ability to read and react to the immediate combat environment. Player commands are "low level" - e.g. "swing weapon", "turn left" - and advanced play involves stringing these actions together fluidly to create combos appropriate for the situation. Time is often measure in frames.
A hack-and-slash is like Diablo or Ys. Combat is still real-time but a lot of strategic planning occurs before combat by preparing weapons and abilities and dexterity does not play as large a role. Player commands are "high level" - e.g. "attack this monster", "cast this spell" - and advanced play involves looking deeper for synergies during planning and managing resource pools (HP, mana). Time is often measured in seconds.
The distinction between the genres is fuzzy and often hard and pointless to determine. Dark Souls is usually called a hack-and-slash but its combat is slow and methodical, and so reading and positioning skills also come into play. Devil May Cry comes from a long line of beat-'em-up designs but still involves ahead-of-time planning in weapon and item choice. Something like God of War seems to sit right between the two terms, with a variety of weapons and long-duration attacks but little lockdown and plenty of cancelling opportunities.