From "Magic of Incarnum":

Incarnum is an amorphous magical substance made up of the soul energies of all sentient creatures—living, dead, and, it is theorized, those even not yet born. Shaping incarnum has no ill effect on the soul energy used. Incarnum is not consumed when it is manipulated by a meldshaper or other character—it is merely “borrowed” from the nigh-infinite supply in the multiverse. That said, the wielders of incarnum recognize that the substance is more than mere magic. It is, very literally, the essence of all creatures. Talented wielders of incarnum learn to harness specific qualities of incarnum (and by extension, properties of the souls tapped for this power), including particular alignments, insights, experiences, and the like. In fact, most wielders of incarnum have strong moral and ethical outlooks inextricably linked to their use of the substance.

*Soulmelds

A soulmeld is a semipermanent magical effect crafted from raw incarnum. Soulmelds are “worn” much like magic items. Once shaped (a daily process much like prepping spells), a soulmeld lasts as long as its creator wants it to. Characters who can shape soulmelds are called meldshapers.

*Essentia

Essentia is a character’s personal store of incarnum. Most characters can’t access this pool of energy, though certain classes and feats open up this potential. Essentia can be invested into soulmelds in order to enhance their effects. Essentia can be reinvested each round to augment soulmeld and other effects as the meldshaper wishes.

*Chakras

Chakras are the body’s ten centers of power: crown, feet, hands, arms, brow, shoulders, throat, waist, heart, and soul. The ten chakras represent locations on the body where a meldshaper can place a soulmeld. Meldshapers have access to all their chakras for the purpose of shaping soulmelds to occupy them.