The term "sin nature" refers to the inherent tendency towards sin that all humans possess as a result of Adam and Eve's disobedience in the Garden of Eden. According to Christian belief, their act of disobedience against God resulted in the fall of humanity, causing them to inherit a sinful nature that is passed down through generations. This means that all people are born with an inclination towards selfishness, greed, anger, and other negative behaviors, which can lead to further sin and separation from God unless they accept Jesus Christ as their savior. In essence, the phrase "sin nature" refers to the innate tendency of humans to do wrong and rebel against God's will.