Completed Metrics Unit

What does the value completed represent as a metric? What are the completed units of measure? Here is a results example with the completed value:

{
id": “160328_3M_S8M”,
“url”: “https://wrap.co/wraps/59e01e34-8a6e-48f2-9828-fd16024d28d8”,
“summary”: “http://www.webpagetest.org/results.php?test=160328_3M_S8M”,
“testUrl”: “https://wrap.co/wraps/59e01e34-8a6e-48f2-9828-fd16024d28d8”,
“location”: “ec2-eu-west-1:Chrome”,
“from”: “Ireland - EC2 - Chrome</b> - 3G</b>”,
“connectivity”: “3G”,
“bwDown”: 1600,
“bwUp”: 768,
“latency”: 300,
“plr”: “0”,
“mobile”: 1,
“completed”: 1459176946,
“tester”: “i-794b8bf5”,
“testerDNS”: “172.31.0.2”

}

Timestamp indicating when the test was completed. For the particular test results you quoted it was 2016-03-28T14:55:46+00:00.