The term "eternal security" refers to the belief that once a person accepts Jesus Christ as their savior, they are guaranteed salvation for eternity and cannot lose it. This means that even if someone who is saved later turns away from God or commits sinful acts, they will still be saved because of their initial faith in Jesus. The concept of "eternal security" is based on the idea that a person's salvation is not dependent on their own actions or works, but rather on the grace and mercy of God.