What does the "cov" mean in a velvet assembler generated contig name?
It means k-mer coverage. From the velvet manual:


  4.2.1 The contigs.fa file
  
  This fasta file contains the sequences of the contigs longer than 2 k
  , where k is the word-length used in velveth.  If you have specified a
  min_contig_length threshold, then the contigs shorter than that value are omitted. Note  that  the  length  and  coverage  information
  provided  in  the  header  of each contig should therefore be
  understood in k-mers and in k-mer coverage (cf. 5.2 ) respectively. 
  E.g.  for a 500bp contig and a k-mer length of 21, the length in the
  header will be 480.