 T-forward measure

For a maturity $T$, the T-forward measure uses the zero-coupon bond maturing at $T$ as numéraire. If $B_t^T$ is its time-$t$ price, an attainable payoff $X_T$ has value $B_t^T{\mathbb{E}}_{Q^T}[X_T\mid {\mathcal{F}}_t]$.