A file format is the structure that tells software how to read, interpret, and store a file. It defines where headers, data, metadata, compression, and optional features belong so different programs can understand the same content. Common examples include JPEG, PDF, ZIP, and ELF.
In cyber security, file formats matter because parsers are complex and often process untrusted input. Attackers can use malformed, oversized, or specially crafted files to trigger bugs in image viewers, document readers, archive tools, or server-side converters. They may also hide data in metadata or rely on differences between parsers. Defenders reduce risk by validating file types, stripping unused features, normalizing content, and using well-maintained libraries with strict size and format checks.