also: ないそん
noun
grandchild from one's son (especially the heir)
Refers specifically to a grandchild born to one's own son, as opposed to a daughter's child (外孫). Often used in contexts of family lineage and inheritance.
長男に内孫が生まれて、家がにぎやかになった。
When my eldest son had a child (my grandchild), the house became lively.
内孫と外孫では、相続の扱いが異なる場合がある。
There are cases where inheritance treatment differs between grandchildren from a son and those from a daughter.
外孫 refers to a grandchild from one's daughter, while 内孫 is from one's son. The distinction is important in traditional family structures.
Compound of 内 (inside, one's own) and 孫 (grandchild). The reading うちまご is the native Japanese reading, while ないそん is the Sino-Japanese reading.