A DNA microarray is a laboratory tool used to study the expression of many genes at once. It consists of a small glass or silicon chip that has thousands of tiny spots, each containing a specific DNA sequence. Researchers can apply a sample of DNA or RNA to the chip, allowing them to see which genes are active in a particular cell or tissue type. By analyzing the patterns of gene expression, scientists can gain insights into various biological processes and diseases. DNA microarrays are commonly used in fields like genomics, molecular biology, and personalized medicine to identify gene functions and potential therapeutic targets.