Christians: What does your Bible or Concordance say is the sin committed in Sodom & Gomorrah?

Homosexuality. When the angels came to Lot's house, the male populace literally asked if they could have sex with them.

Bah, the Bible itself tells you the sin of Sodom: Inhospitality and greed.

Ezekiel 16:49 Behold, this was the iniquity of thy sister Sodom, pride, fulness of bread, and abundance of idleness was in her and in her daughters, neither did she strengthen the hand of the poor and needy.

16:50 And they were haughty, and committed abomination before me: therefore I took them away as I saw good.

Luke 10:10 But into whatsoever city ye enter, and they receive you not, go your ways out into the streets of the same, and say,

10:11 Even the very dust of your city, which cleaveth on us, we do wipe off against you: notwithstanding be ye sure of this, that the kingdom of God is come nigh unto you.

10:12 But I say unto you, that it shall be more tolerable in that day for Sodom, than for that city.

There was more than one sin committed by them; they were corrupt. It does mention though that there was an abundance of homosexuals that came, beating on Lot's door trying to get to the angels.

Primarily homosexual sex. The Hebrew word for "to know" is "yada". In many cases it means to know intimately like here:

Gen 4:1 ¶ And Adam knew Eve his wife; and she conceived, and bare Cain, and said, I have gotten a man from the LORD.

It is used in the same regard here involving Siodom here:

Gen 19:5 And they called unto Lot, and said unto him, Where [are] the men which came in to thee this night? bring them out unto us, that we may know them.

You must mean commentary, a concordance will only tell you where the word is.

for this cause God gave them up unto vile affections for even their women did exchange the natural use for that which is

against nature and likewise also the men leaving the natural use of the womam burned in their lusts one toward another

, men with men working that which is unseemly and receiving in themselves that recompense of their error which was fitting

and even as they did not like to retain God in their knowledge , God gave them over to a reprobate mind

It was all types of immorality: homosexuality, lasciviousness, idolatry, etc.

Well, we know what SODOMY is...

But I'd have to try and figure out what is it to be GOMORRAHED by someone.

It doesn't go into specifics.