As two examples: Partial trust means you trust a key for different purposes, or for different levels of validity. Different purposes: "Do I trust that this key

As two examples: Partial trust means you trust a key for different purposes, or for different levels of validity. Different purposes: "Do I trust that this key correctly identifies this person?" is a separate question from "Do I trust this person to do proper verification before signing others' keys?" (i.e., trusted link in the Web of Trust) Different validity: "I've met this person and verified they own the key", is different from, "They've identified themselves with two forms of government ID", is different from "I've known them all my life".