abort terminates an observation started by run and similar commands. The observation is not saved to disk. If abort is given when there is no observation then it will `succeed' but will have no effect.
abort
CCD readouts cannot be aborted (due to a fundemental hardware-design fault in the CCD controllers). Hence, giving the abort command during a readout is pointless and the results may be confusing. In general, abort 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 abort' 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 abort was run before the end of CCD readout.