The word "lifelong" means something that lasts for an entire lifetime or throughout one's life. It can refer to a lifelong commitment, such as a marriage vow, or a lifelong passion, like a love of learning. The term is also used in reference to conditions or habits that begin early in life and continue into old age, such as lifelong smoking or obesity. In essence, "lifelong" describes something that lasts for the entire duration of one's existence.