What kind of relative is considered unrelated?

Step brothers and sisters, adopted siblings, and in-laws are examples of biologically unrelated family members.

Well let's look at it this way. By the law of probability we are all related. Now we no doubt will never find the documents to back it up.

Many people today will reach the time of Charlemagne in some of their family lines in 40 generations. You will in some sooner and in some later. 40 generations are your 2 parents, 4 grandparents, and up through you 38xgreat grandparents. Since it doubles up each generation you go back it begins to pyramid big time. If each of those 38great grandparents were a different person they would total over 1 trillion, 162 billion people. The population of the world at the time is estimated to have been from 210 to 230 million people and of course far less for Europe. So if you are married your spouse is probably a cousin. It is just a matter of how many times she is a cousin and if you can get back far enough to find the documentation to prove it. Your parents are no doubt cousins.

I might add in the U.K. and in many U.S. states first cousins are allowed to marry. Other states will allow marriage between 2nd cousins.

However as you walk down the street just say, "Hi Cuz" to everyone you pass and you will probably be right.

All relatives are related, so your question is contradictory.

A non-relative is someone who does not have a common ancestor, typically meaning "in genealogical timeframe".

In my own case, I never met all of my aunts, uncles, or first cousins; I don't even know the names of second cousins, but through Family Tree DNA I "met" an 8th cousin, twice removed (same ancestress back in the early 1600s). But, a good question: noormally speaking, a non-relative would be considered to be anyone you do not know the relationship of; after all, supposedly we are all related.

Un-relative: sounds like the concept of "un-friending" on FaceBook. Also sounds like a standard mother-in-law joke. A lot of people would be interested in that!

Genealogy is based primarily on genetic inheritance, but it is also highly concerned with individuals and their dreams, achievements, ambitions and personal history. As a result, adopted people, aunts and uncles through marriage, family friends, etc., are all important as they can reveal information about the development of the individuals and their subsequent families. Such genetic "un-relatives" are often crucial in human migration patterns.

The key is to simply designate their relationship to the family. If there's a genetic link, it will show on charts. If it is a married relationship, that can be shown on charts, too, as an "uncle through marriage" or as an in-law. Important friends can always be explained in notes and family histories. Just describe the nature of the relationship adequately and you'll be fine.

Now, about my mother-in-law...

Although there is not such term used in genealogy, any one who is not a blood relations is not related.

So the spouses of your siblings are not related. The cousin question pops up every once in a while, and it you share a common relative like your 19th Great-Grandfather is their 15 Great-Grandfather are the same person - you are related, it is tracing the bloodlines.

"unrelated" by what standard. Not blood related? That would be anyone that is related only my marriage. (ie the uncle that is only an uncle because they are married to your blood related aunt)

For legal purpose (ie not considered incest)? Depends on the state in some states 1st cousins are not considered incest in others they are but anything more distantly related are. Just for you to consider them not related? That is up to you.

No blood ties...so married into the family