Microarrays are laboratory tools used to study gene expression and genetic variations. They consist 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 measure the activity of many genes at once. By analyzing the patterns of gene expression on a microarray, scientists can gain insights into how genes function in different conditions, such as in diseases like cancer or diabetes. This technology has revolutionized fields like genomics and personalized medicine, enabling more targeted treatments based on individual genetic profiles.