What is expiry time represents in this format

I see the output. root@X10SDV-8C-TLN4F:/mnt/config# cat /var/lib/libvirt/dnsmasq/mgmt-1br1.status [ { "ip-address": "192.168.27.8", "mac-address": "52:54:00:42:21:14", "hostname": "vyatta", "expiry-time": 1589500228 } ] Can you please explain what does the expiry-time mean ? What are its units ? Please let me know. Thanks & Regards Santhosh Kumar Gunturu