...B

The spatial frequency of the observation is: $k=B/\lambda$, where $\lambda$ is the observing wavelength. The units of k are cycles/radian if $\lambda$ and B have the same units.

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... disk

In practice this will be easiest for disks that are seen not too far from pole on, so their image has a high degree of azimuthal symmetry. This limits the number of baselines needed, and requires the measurement of visibility amplitude only, since all phases will be approximately 0.

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... baseline

The visibility is the ratio of the correlated flux and the total flux ( $F_{{\rm cor}}/F_{{\rm tot}}$). The correlated flux, or correlated spectrum in the case of a spectrally dispersed measurement, is the quantity an interferometer measures.

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