A "cell-specific gene" is a term used to describe any gene that is expressed at different levels in various cells of an organism. Synonyms for this term include "tissue-specific gene", "organ-specific gene", "cell-type-specific gene", and "cell-line-specific gene". These terms refer to the same concept of genes that are selectively activated or repressed in specific cells or tissues, and not in others. The identification of these genes is crucial to understanding cell differentiation, development, and disease pathology. Studying cell-specific genes can lead to new diagnostic tools and therapeutic targets for various diseases.