look,
I'd classify carry heroes like this:
hard carry:
a carry whose goal is to get every single bit of gold on the map for the first 30 minutes watching only his ass, ksing, farming, getting towers, avoiding any chance of death, then after as needed he continues farm or w/e
hero example is dusa, clinkz, void, spec
ganking carry (semy carry):
a carry whose goal is to obtain few items by farming mid until level 6-7-8, then ganking sides thus obtaining gold from kills, these heroes usually have a big spell damage output in combination of mid-latte game potential
heroes: potm, tinker, sf, pugna, viper, storm...
spell spamming carry (semy carry):
a carry that usually obtains some tanking items to ensure himself of casting spells as long as possible, he farms along the way and helps in team fights when he can
heroes: best example is necro, other good example is undying, krobe maybe, pugna(ganking-spellspaming-semy carry xDDD)
tanking carry (semy carry):
well this is similar to spell spamming carry just his main role is to go in first and be that guy around whom all the enemy heroes gather so you can place your spells more efficient in a fight
heroes: slardar, alcemist(kindof combination of tank and hard carry), axe, cent
I may failed horribly, but this is as I see it