FUD stands for "fear, uncertainty, and doubt". A term popularized as a traditional public relations tactic designed to shift public perception about a product, technology, or candidate by releasing information such that a negative emotional response is excited.
FOMO or "Fear of missing out" is generally used when markets are taking off. FOMO can lead to emotional trading and bad decision making.
Diamond Hands is a meme that highlights the importance of HODLing.
HODL is the most popular crypto slang, pronounced "Hoddle", simply means to buy and hold for a long time.