The term "God" herein assumes that the Supreme Being, our Creator, and our Judge (guy who dispenses rewards & punishments) are for all practical purposes identical.
Good is that which is liked. It is a subjectively evaluated term. That which is liked either increases happiness or decreases unhappiness.
If God likes something, that thing is objectively good, but still may be subjectively bad relative to any created evaluator. God is objectively good if, and only if, he likes himself. He is not automatically good just because he's God.
Some theists like to use good as a noun, and say God and that noun are identical. The same theists like to say God is truth; God is love; God is whatever emotionally positive thing they happen to be talking about. This mushing together of concepts destroys the epistemic meaning of those concepts, and makes the terms labeling them useless for all practical purposes. It is therefore an epistemic error, therefore erroneous theology. Their God is an epistemic black hole into which concepts fall and become meaningless.
To say "God is good", means either that he is objectively good because he likes himself, or he is subjectively good because the person making the statement just happens to like him.
Note that God would be objectively good if he enjoyed torturing babies, and did so constantly, and never compensated them for having done so. He would be objectively good even if the entire created order hated him. So what does objective good or objective goodness mean to any living thing? Nothing. It probably doesn't even mean anything to God.
It is, however, useful as a polemic for theists to use against atheists, who can legitimately be called axiological nihilists, since they have no objective referent for goodness, or its subset, morality. Atheists will continue to be beaten up with this stick until they figure out an alternative objective referent for morality. Yes, one actually exists. It is the ratio of happiness to unhappiness in the universe – an objective fact which would remain objective whether the Supreme Being likes it or not. Of course the Supreme Being can change that ratio if he doesn't like it, by making creatures happier or unhappier. But he cannot change the objectivity of the fact that the ratio is what it is at any given time – or for all time.There are two possible objective referents for good:
2. the ratio of happiness to unhappiness in the universe
There are two possible objective referents for morality:
2. willful behavior which causes a greater ratio of happiness to unhappiness in the universe
God is objectively good(1) or moral(1) even if he creates only universes in which there is more unhappiness than happiness.
God is objectively good(2) or moral(2) relative to a particular universe if, and only if, he creates more happiness than unhappiness in that universe.
Most monotheists (and virtually all scriptural monotheists) worship (or at least acknowledge) a God whom they claim to be good(2) and moral(2) because he is good(1) and moral(1). This is a gross error, which has historically proven to cause all manner of travesties up to and including religious terrorism.