= Solution
A <multi-slit spectrograph> uses a focal-plane mask containing slitlets at the target positions, or movable slitlets placed there. Each transmits its target and nearby sky into the <collimator>; a <diffraction grating> or other disperser produces a separate <optical spectrum> on the detector. The layout must avoid overlap between spectra, and the length of a slit allows local sampling of <sky brightness> and sometimes spatial information within the target.
A <fiber-fed spectrograph> places <optical fibers> at target positions in the telescope focal plane. The fibers carry the selected light to a spectrograph and their outputs are lined up as a pseudo-slit. The spectrograph can be mechanically stable and separate from the telescope's focal plane. Additional fibers aimed at blank sky provide a simultaneous estimate of <sky brightness>; fiber positioning, coupling losses, transmission, and <focal-ratio degradation> must be accounted for.
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