Hey kiddo, have you ever heard of the word "inheritance?" It's when someone passes on their money or property to someone else when they die. Well, secundogeniture is a fancy word for a special type of inheritance rule that used to exist in some families a long time ago.
You know how usually the oldest kid gets everything when their parents pass away? Well, secundogeniture was a rule that said the second oldest kid also gets some important things - like property or money - when their parents die.
This rule was usually only followed by really rich and powerful families. The oldest kid would still get most of the inheritance, but the second oldest would get a nice chunk too. This was meant to make sure that the family's wealth stayed in the family, even if the oldest kid wasn't very responsible with it.
Nowadays, this type of inheritance rule isn't used as much anymore. Most families just follow a simple "oldest kid gets everything" kind of rule. But, it's still interesting to learn about how some families in the past used to divide up their property when someone passed away.