I'm ambiguous about it because I'm describing EY's usage of the word, and he's been ambiguous about it.
I typically adapt my usage to the person who I'm talking to, but the way that I typically define "good" in my own head is: "The subset of my preferences which do not in any way reference myself as a person"...or in other words, the behavior which I would prefer if I cared about everyone equally (If I was not selfish and didn't prefer my in-group).
Under my usage, different people can have different conceptions of good. "Good" is a function of the agent making the judgement.
A pebble-sorter might selfishly want to make every pebble pile themselves, but they also might think that increasing the total number of pebble piles in general is "good". Then, according to the Pebblesorters, a "good" pebble-sorter would put overall-prime-pebble-pile-maximization above their own personal -prime-pebble-pile-productivity. According to the Babyeaters, "good" baby-eater would eat babies indiscriminately, even if they selfishly might want to spare their own. According to humans, Pebble sorter values are alien and baby-eater values are evil.
There seems to be a widespread impression that the metaethics sequence was not very successful as an explanation of Eliezer Yudkowsky's views. It even says so on the wiki. And frankly, I'm puzzled by this... hence the "apparently" in this post's title. When I read the metaethics sequence, it seemed to make perfect sense to me. I can think of a couple things that may have made me different from the average OB/LW reader in this regard: