Well it's the word gay "marriage" proponents used for what they claim was a marriage. Gay "marriage" is a marriage like a bicycle is a motorcycle. If you think your bicycle is a motorcycle and I say to you, go get your bicycle, you wouldnt know what I was referring to. I would have to use the word "motorcycle" even though it's actually a bicycle.
I feel sorry for you, that you cannot understand that there are many things that are mere human constructs, and as such, fall on the definitions humans give to them. Where this involves matters considered legal, then laws are made and definitions provided. For example, Canada makes no law concerning marriage from the ecclesiastical standpoint, except to say that no church can make a marriage that is NOT legal under Canadian law. And in Canadian law, "Marriage, for civil purposes, is the lawful union of two persons to the exclusion of all others." So a church may, if it chooses, marry a man and a woman, or two men or two women.
A church may decline to marry a same-sex couple, but no civil authority may if there is no other bar to the marriage.. But no church may declare such a civil marriage to be invalid, except within the church itself, which is of no effect outside of said church.
In 1967, when I was already 19 years old, the Supreme Court, in Loving v. Virginia, a unanimous Court struck down state laws banning marriage between individuals of different races, holding that these anti-miscegenation statutes violated both the Due Process and the Equal Protection Clauses of the Fourteenth Amendment. Luckily for Justice Clarence Thomas, who by the way would like to ban same-sex marriage again.
We all know what a bicycle is, and we all know that it is in one way different from a motorcycles (the mode of propulsion) -- and yet nobody has any difficulty at all calling them both "bikes." When a teenager with a bag of newspapers says he's going to get his bike, we do not interpret that in quite the same way we do when a scruffy, leather-clad dude with artwork all over his body says he's going to get his bike.
How, I wonder, does it actually impact you personally, that two men (say Pete Buttigieg and Chasten Buttigieg), or two women (say Ellen DeGeneres and Portia de Rossi) are married? If marriage is good for people (and I think it is) how does those couples' taking advantage of that good harm you? What interest or stake do you have in those good people finding their own happiness, meaning and security in their own way?