What defines a compact symmetric object? A carefully vetted sample of
  CSOs
  Compact Symmetric Objects (CSOs), young jetted-AGN of overall projected size
<1 kpc, are of great interest due to their youth and evolution. The
classification was introduced to distinguish between ~95% of powerful compact
extragalactic radio sources in flux density limited samples that are dominated
by asymmetric emission due to relativistic beaming from jets aligned close to
the line of sight, and ~5% of objects that are not. The original classification
criteria were: (i) overall projected diameter smaller than ~1 kpc, (ii)
identified center of activity, and (iii) symmetric jet structure about the
center. There is confusion and erosion of the value of the CSO classification
due to misclassifications. Many jets contain compact bright features outside
core, resulting in a GPS total spectrum and a "compact double" appearance, and
some objects with jet axes aligned close to the line of sight appear symmetric
because the approaching jet is projected on both sides of the core. To
eliminate the confusion, we propose adding (iv) slow radio variability and (v)
low apparent velocity of bright features moving along the jets to the above CSO
criteria. We are compiling a catalog of CSOs using these five criteria to
eliminate the confusion of Doppler boosting.
