Triangulation
There is a lot of confusion on what triangulation means as well as its purpose.
Some experts claim that when three people show DNA matches, they are an example of triangulation.
Other experts state that the three individuals must share DNA on the same segment of the chromosome. This last statement is very important because triangulated segments are probably inherited from a common ancestor. Triangulation can also involve more than three individuals, but the minimum number is obviously three.
Triangulated matches that are not on the same segment could have been inherited from different ancestors that are not common to the three individuals who are being compared.
We must remember that it is possible to share a small amount of DNA with someone and not be related. For example, I share a very small amount of DNA with Neanderthals just like millions of other individuals but I am not related either to a Neanderthal nor to the millions of other people who share Neanderthal DNA.
The link below from GEDmatch explains triangulation very well with examples and could be helpful to understand the concept:
https://dna-explained.com/2020/01/23/triangulation-in-action-at-gedmatch/
