JMdict: 1465660

入れ子 【いれこ】

1. [n] nest (of boxes); nesting
2. [n] concealed information
3. [n] nested structure
4. [n] adopting a child after one's own has died; child adopted by a parent of a deceased child
5. [n] cavity in an oar (fitted onto a peg as part of a traditional oarlock)