Basic
ISP = Internet Service Provider
VPN = Virtual Private Network — more info
Adversary = an attacker; a threat to your privacy and/or security endeavors
Cryptography = the practice and study of techniques for secure communication in the presence of third parties called adversaries — more info
Threat model = a model of the most probable threats to your security/privacy endeavors. — more info
Message = any data in the context of cryptography; usually data that is to be encrypted — more info