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 RNA is applied to the microarray, it binds to complementary DNA sequences, allowing researchers to measure gene activity and understand how genes respond to different conditions. These tools are valuable in various fields, including genomics, molecular biology, and medical research. By analyzing the data from microarrays, scientists can identify genes associated with diseases, track changes in gene expression, and develop targeted therapies for conditions like cancer.