A symlink, short for symbolic link, is a filesystem object that points to another file or directory. To the operating system, it looks like a path shortcut: when a program opens the link, it follows the target path instead.
Symlinks matter in security because they can break assumptions about what file is really being modified. If software checks a path and then later uses it without care, an attacker may replace it with a symlink and redirect reads, writes, or permission changes to a different file. That can expose sensitive data, overwrite protected files, or trigger privilege escalation. Defenders reduce this risk by using safe file-handling APIs, verifying paths before and during use, and refusing to follow unexpected links in privileged operations such as chmod, backup, or update routines.