Glossary
SUID & SGID bits
Special permission bits that let an executable run with the privileges of its owner or group rather than the calling user.
SUID (Set User ID) and SGID (Set Group ID) are special permission bits on executable files. When set, the program runs with the privileges of the file's owner (SUID) or group (SGID) instead of those of the user who launched it. This is how an ordinary user can run tools like passwd that need root access to system files.
Because a vulnerable SUID-root binary can give an attacker full privilege escalation, hardening involves auditing them, for example with find / -perm -4000 -type f, and removing the bit where it is not strictly required.