Disk space refers to the amount of storage capacity available on a computer's hard drive or solid-state drive. It is measured in units such as gigabytes (GB) or terabytes (TB), indicating how much data can be stored. Disk space is essential for saving files, applications, and the operating system itself. When disk space runs low, it can affect a computer's performance and limit the ability to save new files. Users can manage disk space by deleting unnecessary files, using external storage devices, or utilizing cloud storage services like Google Drive or Dropbox to free up space.