I bet your definition is drastically different from God’s.
Without a doubt the Old Testament city of Sodom was immoral and deserving of her judgment sent by God. Genesis records, “Then the Lord said, ‘The outcry against Sodom and Gomorrah is so great and their sin so grievous that I will go down and see if what they have done is as bad as the outcry that has reached me’” (Genesis 18:20-21).
What was Sodom’s “grievous sin”?
There is an interesting story in Jewish folklore about Peletith, one of Lot’s daughters. According to the story, Peletith married a high ranking official of Sodom. Every day when Peletith would go draw water she saw a poor man sitting by the well. She had compassion on the man and started sneaking him provisions from her house. The men of Sodom began to wonder how the poor man was surviving and when they investigated the matter they discovered Peletith had been taking care of him. Angry with her compassion, the men had Peletith burned by fire. Before she died, Peletith prayed, “Sovereign of all the worlds, maintain my right and my cause (at the hands of) the men of Sodom.” According to the story her prayer was the outcry God heard that caused Him to act against Sodom.
The rest of the biblical story is full of depraved behavior by the men of Sodom. But as sinful as that depraved behavior was, it was not their most “grievous sin.” The prophet Ezekiel clearly explains Sodom’s sin when he said, “Now this was the sin of your sister Sodom: She and her daughters were arrogant, overfed and unconcerned; they did not help the poor and needy. They were haughty and did detestable things before me. Therefore I did away with them as you have seen” (Ezekiel 16:49-50). The grievous sin of Sodom was their refusal to take care of the vulnerable and disenfranchised among them! Their grievous sin was injustice! Instead of caring for the “least of these” the people of Sodom fed their own greedy, fleshly, selfish, sexual, consumerist appetites, and were judged accordingly. Sodomy, at least partially, could be defined as the absence of social-justice in the community. Sodomy, however it is defined, is a serious violation against the character of God.
 The story and destruction of Sodom is found in Genesis 18:16-19:29.
 The Old Testament does not mention the names of Lot’s daughters. The story of Peletith is part of Jewish tradition and folklore. There is no way to know the historical reliability of the story, but it is an interesting story none-the-less.
 The story of Peletith is part of a collection of ancient rabbinic homilies that incorporates folklore, historical anecdotes, and moral exhortations. This particular story comes from an 8th century midrashic teaching entitled Pirke de Rabbi Eliezer. More information can be found at http://www.jewishencyclopedia.com/articles/12185-pirke-de-rabbi-eli-ezer.
 Italics added for emphasis.
 This is how Jewish scholars have interpreted the story of Sodom for thousands of years.