Malware
Any software intentionally designed to cause harm to a computer, server, or network, including viruses, ransomware, and spyware.
Malware↗ (short for "malicious software") is a broad umbrella term for any software intentionally designed to cause harm, gain unauthorized access, or disrupt a computer, server, or network. Viruses, worms, ransomware↗, spyware↗, and trojans are all different categories of malware, each with a different method of spreading and a different goal.
Malware typically gets onto a device through phishing↗ emails, malicious downloads, infected USB drives, or by exploiting an unpatched software vulnerability↗. Reputable antivirus↗/anti-malware software, keeping systems patched, and being cautious about what you click or install remain the core defenses against the vast majority of malware infections.