From csoonline.com
Steganography is a millennia-old concept that means hiding a secret message within an ordinary-looking file that doesn’t raise any suspicions. The word has Greek roots, being a combination of steganos, which translates to “concealed, protected,” and graphein, which means “writing.”
APT groups, ransomware gangs, and other threat actors often hide information when attacking a target. For example, they might conceal data when exfiltrating it, cloak a malicious tool, or send instructions for command-and-control servers. They could put all this information in unassuming image, video, sound, or text files.