Haptens are small molecules that are not immunogenic by themselves. When they bind to larger molecules, like proteins, they become immunogenic and elicit an immune response. Haptens are commonly found in a variety of things like drugs, chemicals, and heavy metals. Some synonyms for the word "hapten" include incomplete antigens, partial antigens, and minimal antigens. These terms all convey the same idea that haptens are not capable of eliciting an immune response on their own and require association with a larger molecule. The study of haptens and their role in immunology is important for understanding how the immune system responds to foreign substances and how it can be manipulated for therapeutic purposes.