Trojan:
A Trojan, or Trojan Horse, is more of a delivery method for infections than an infection. The Trojan presents itself as something useful to trick users into opening it. Trojan attacks can carry just about any form of malware, including viruses, spyware, and ransomware. Famously, the Emotet banking Trojan started as an information stealer, targeting banks and large corporations.
Later, Emotet operated purely as an infection vector for other forms of malware, usually ransomware.