Attributes are hidden characteristics of Servants and other characters that work much like the Class triangles, with some attributes being more or less effective versus another. A brief explanation of attributes is given by Da Vinci in London, Chapter 3. They are more thoroughly explained in Emiya's interlude "To be a Master."
Human: Servants with the Human attribute are Servants whose powers are drawn form great deeds they accomplished throughout history such as The Roman Emperors or the Hassans.
Earth: Servants of the Earth attribute are Servants who frequent myths and legends and typically include the more monstrous or fanciful servants.
Star: Servants of the Star attributes are "the hopes of mankind" and whos actions shaped humanity's destiny.
Beast: Beasts are entities classified as the Evils of Man, commonly referred to as the Beasts of Calamity. They exist to bring about the annihilation of Mankind and threaten the continuity of history.
The damage multiplier relationships between each attribute are summarised in the table below: