What Does Worm Mean?
A worm is a type of malicious software (malware) that replicates while moving across computers, leaving copies of itself in the memory of each computer in its path.
Techopedia Explains Worm
A worm locates a computer’s vulnerability and spreads within its connected network like an infection, while continually seeking new vulnerabilities. Like viruses, worms often originate from e-mail attachments that appear to be from trusted senders. Worms then spread to a user’s contacts via his e-mail account and address book.
Some worms spread and then do nothing while tthers cause harm. In such cases, the worm’s code is known as payload.