expire_time is the time left until the timer expires. The TCP stack in the Linux kernel supports a number of timers, and they all have an expiration time.
retrans is the number of retransmissions which have occurred. TCP implementations retransmit packets they believe have been lost; they counts these retransmissions so that they will know when to give up. You shouldn’t see this too often; one way to force it is to try to open a connection on a port which isn’t rejected immediately, e.g. (based on an example in one of your previous questions):
If you run that, you’ll see
curl sitting there for a while, and
ss -o will show a
SYN-SENT entry with an increasing retransmission count. You’ll also see the back-off applied in such circumstances: the initial expiration time will increase every time the packet is retransmitted.