Imagine you have a big family with a lot of relatives, like grandparents, aunts, uncles, cousins, and so on. Each of them could have different names depending on how they are related to you. For example, you might call your grandmother "Nana", but your cousin might call her "Grandma". This is what we call "kinship terms".
Now, in some cultures, these kinship terms can change based on different factors like age, gender, and number of relatives. For example, if you have two grandmothers, one might be called "Nana" and the other might be called "Granny". Or, if you have a younger brother, you might call him "little brother", but if you have an older brother, you might call him "big brother".
All of these variations in kinship terms are important because they help us to show respect and acknowledge the different relationships we have with our family members. They can also be a way to show hierarchy and age differences within the family.
Overall, numerical variation in kinship terms means that we use different names to refer to our family members based on how many of them there are, their age, and other factors. It can be a bit confusing, but it's a way to help us better understand our family relationships and show respect to those we love.