What is the correct term for a piece of malware that hides inside a legitimate software program or file from trusted sources

Trojan horse

Explanation:

Based on the Greek legend of how Greek soldiers hid in a Trojan horse to infiltrate and destroy Troy from within, Trojan horse malware mirrors this attack when attacking software.

It hides inside and disguises itself as a legitimate software program or a file from a trusted source and then when clicked on, it works to infect the software.