A Trojan Horse is a malicious software that disguises itself as a harmless program to fool users into downloading and installing it. It's named after the mythological Trojan Horse used by the Greeks to sneak into Troy and win the war. There are several synonyms for the term "Trojan Horse," including malware, virus, spyware, backdoor, rootkit, phishing, and ransomware. These words are often used interchangeably to refer to any software that infects a computer system without permission or knowledge. It's important to use proper antivirus software and avoid downloading suspicious files or clicking on unknown links to prevent falling prey to these malicious software.