DNA microarrays are laboratory tools used to study the expression of many genes at once. They consist of a small glass or plastic slide that has thousands of tiny spots, each containing a specific DNA sequence. When a sample of DNA or RNA is applied to the slide, it binds to the complementary sequences, allowing researchers to see which genes are active in a particular cell or tissue. These microarrays can help scientists understand diseases, identify genetic variations, and discover new drugs. By analyzing the patterns of gene expression, researchers can gain insights into how genes interact and contribute to various biological processes.