TrueType, usually seen as the .ttf extension, is a standard font file format used by operating systems and applications to render text consistently. In normal use, it is harmless and common, which is exactly why attackers sometimes abuse it as camouflage in email attachments. A file labeled as a font can appear routine to a user, helping a malicious attachment avoid quick suspicion.
In cyber security, the important issue is that the extension does not prove the content is safe. A disguised or renamed attachment may contain a script, archive, or other payload that launches a loader or another stage of malware after the file is opened or unpacked. Defenders therefore inspect behavior, not just filenames: email filtering, attachment detonation, sandboxing, and alerts for unexpected script execution or suspicious child processes can expose this tactic. A .ttf label is not evidence of safety; it is only a filename.