Each endowment token holds a 1:1 claim on a real asset in Aave; the principal never leaves, only the yield moves.
An endowment token is backed 1:1 by a real asset — USDC, WETH, or cbBTC — held in Aave. The backing earns lending yield. The principal itself stays put: it is the endowment, and an endowment is defined by never spending its corpus, only what it earns.
When the yield is harvested it is split three ways by the three-leg yield split — the same way for every endowment token. One third deepens liquidity, one third fans across the family, one third flows to the causes the members vote on.
Because the principal is held in Aave and never withdrawn to spend, the network can give forever from the yield without ever drawing down what backs the tokens. That is the whole idea of an endowment, expressed on-chain.