Retired out
"We batted poorly and set too low a total.

The opposition's opener knocked up a big score in no time. With the winning line in sight, he said he would 'give someone else a go', and walked off. Things then promptly turned round and wickets started to fall very quickly.
At the fall of their 'last' wicket, with only eight runs needed, the batsman who had retired marched out to the middle to resume his innings. Our captain objected to this, and so we won the match.
But what is the Law about 'retiring'?"

If he retires through illness, injury or any other unavoidable reason, a batsman may resume his innings later, when a wicket falls, if he's fit to do so. But if he chooses to retire, as here, he is recorded as Retired out.

He can resume his innings only if the fielding captain agrees - and he's not obliged to consent.

Read more about Law 25 (Batsman's innings; Runners) at the MCC website