1. Status and appellation: Great-grandfather Hu is a higher-ranking elder in the family, referring to the ancestors or elders of the family, while Great-grandfather Hu is the third-generation elder in the family, with a lower status and a different appellation from the clan.

2. Blood relationship: Grandpa Hu is the ancestor of the whole Hu family or the elder of earlier generations, and has direct blood relationship with more family members, while Grandpa Hu is the third generation elder of the whole family and has distant blood relationship with family members.