外孙子 refers to a person's grandson or granddaughter from their son or daughter.
Topic 1.1: 1.1 Families and Communities in China
外孙子 (wàisūnzi) cheat sheet for homework
爷爷 (yéye): This term refers to one's paternal grandfather.
奶奶 (nǎinai): This term refers to one's paternal grandmother.
孙子 (sūnzi): This term refers to one's grandson.