What's the meaning of variable "clientVersion"?

[ccconnor]

The variable "clientVersion" is compared with REQUIRE_VERSION(which is a protocol version) in the function IsGood,

if (clientVersion && clientVersion < REQUIRE_VERSION) return false;

while it is compared with 31900(which seems to be a client version v0.3.19) in the function GetBanTime.

if (clientVersion && clientVersion < 31900) { return 604800; }

I'm confused. What on earth should "clientVersion" be compared with? Client version or protocol version?
This is the output of bitcoin-cli.

$ bitcoin-cli getnetworkinfo
{
  "version": 170100,
  "subversion": "/Satoshi:0.17.1/",
  "protocolversion": 70015,
......
}

Looking forward reply. Thanks!