ZIP

In short: A widely used, lossless format for compressing and bundling several files into an archive.

In more detail: Practically every operating system can natively open ZIP files, which makes it the de-facto standard for file exchange. Usually achieves somewhat lower compression ratios than more modern formats like 7-Zip, but with maximum compatibility.

In Depth

The ZIP format was developed back in 1989 and has since become so widespread that Windows, macOS and most Linux distributions can open and create ZIP files without additional software — a decisive advantage over formats like 7-Zip (.7z) or RAR, which often achieve better compression ratios but require additional programs to unpack. Exactly this compatibility advantage explains why ZIP has remained the standard for general file exchange to this day, despite technically superior alternatives.

Internally, a ZIP file consists of individually compressed entries (every contained file is compressed on its own, not the entire archive content at once), plus a central directory at the end of the file, listing which files are contained and where they sit in the archive. This structure allows individual files to be specifically read from or replaced in a large ZIP archive, without having to rebuild the entire archive — one reason many other file formats (.docx, .xlsx, .jar for Java, even some graphics formats) are internally simply ZIP archives with their own folder structure, instead of inventing a completely new binary format.

ZIP also optionally supports password protection, where the older standard encryption still active in many tools (ZipCrypto) is considered cryptographically weak and comparatively easy to crack — for genuinely sensitive data, the stronger AES encryption should be used instead (supported by newer ZIP tools, but not standard everywhere), or a separate encryption tool like GPG should be used.

See also: 7-Zip, Compressing