cDNA, or complementary DNA, is a form of DNA synthesized from a messenger RNA (mRNA) template through a process called reverse transcription. This technique is commonly used in molecular biology to study gene expression, as it allows researchers to create a stable DNA version of the mRNA present in a cell at a specific time. Researchers often use cDNA in various applications, including cloning, sequencing, and quantitative PCR (qPCR). By converting mRNA into cDNA, scientists can analyze the genes that are actively expressed in a cell, providing insights into cellular functions and responses to different conditions.