From GuildWiki

A fleshy creature is a creature made of flesh, which makes it vulnerable to bleeding, poison and disease. Most creatures are fleshy.

Only the corpses of fleshy creatures can be used for a Necromancer's corpse exploitation spells.

The following creatures are not fleshy:

• Celestial creatures
• Elementals (except for Roaring Ethers)
• Some Enchanted (Enchanted Bows, Enchanted Hammers and Enchanted Swords)
• Graven Monoliths
• Golems
• Jades
• Some Titans, including all Titans exclusive to the Realm of Torment
• Nightmares
• Phantoms (but not the similar looking Krakens)
• Ooze
• Reed Stalkers (but not other Stalkers)
• Spirits (also immune to all other conditions, except Burning)
• Stone Guardians
• Some Undead, including all Skeletons and all Minions except for Flesh Golems
• Some or all Ghosts

For more information about target categories, see also: Target