Eurasian Adam is a term used in genetics to refer to the hypothetical ancestor from whom all living humans in Eurasia (which includes Europe and Asia) can trace their lineage back to. Scientists believe that this person lived around 70,000 years ago and was part of a group of humans who migrated out of Africa and eventually settled in Eurasia.
Think of it like a family tree. Just like you have parents, grandparents, and great-grandparents, your ancestors also had ancestors of their own. Scientists have traced back the family tree of all humans in Eurasia to this one person, who is now called Eurasian Adam. He is not a real person, but rather a symbol for the first person in this lineage.
By looking at the DNA of people from different parts of Eurasia, scientists can tell that their ancestors all came from the same group of humans that migrated out of Africa. This is why they believe in the existence of Eurasian Adam. It's also important to note that this ancestor is different from the biblical Adam, who is a religious figure and not based on scientific evidence.