ATAC-seq, or Assay for Transposase-Accessible Chromatin using sequencing, is a technique used to study the accessibility of chromatin in the genome. It identifies regions of DNA that are open and available for transcription, which can indicate active regulatory elements such as enhancers and promoters. This method involves using a transposase enzyme to insert sequencing adapters into accessible regions of chromatin. The resulting data provides insights into gene regulation and cellular function. By analyzing the patterns of accessibility, researchers can better understand how genes are turned on or off in different cell types or conditions, contributing to fields like genomics and epigenetics.