killmult terminates an sequence of observations started by multrun and similar commands. The current observation is not saved to disk and all unstarted observations in the sequence are cancelled.
killmult
CCD readouts cannot be aborted (due to a fundemental hardware-design fault in the CCD controllers). Hence, giving the killmult command during a readout leaves the system temporarily unable to observe again. In general, killmult may complete quickly, but the system won't be able to start a new observation until the readout finishes.
The statement that `the data are not saved to disk after killmult' needs qualification. Data are written to disk at various points during an observation, so some saving will usually have happened. In general, the glance file will be partially written but may not be a valid FITS-file. The glance file will not have been renamed to an archive or scratch file if killmult was run before the end of CCD readout.