There are multiple definitions:

1. center of gravity(English)

   • Biophysics

2. cluster of orthologous groups(English)

   • phylogenetic classification of proteins encoded in complete genomes; each COG includes proteins that are inferred to be orthologs (direct evolutionary counterparts)
   • Genomics, Gene cluster, Classification, Evolution & development
   • http://www.pdg.…/summary/7.html

3. Children's Oncology Group(English)

   • Pediatrics, Oncology
   • https://doi.org…2045(17)30355-8