The Free On-line Dictionary of Computing (30 December 2018):

10base5
thicknet

    An Ethernet network cabling specification
   operating at ten Mbps, "baseband" (as opposed to radio
   frequency), and with a maximum single cable length of 500
   metres.  This is normally carried on RG8 cable.

   Compare 10base2, 10baseT.

   (2002-06-17)