I understand what a carry does(being carried at first, then carry its team to victory).
What I don't understand is what a half-carry (or semy-carry) does. What are the main differences between the two?
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: