Informal terms are words or phrases that are used in casual conversation rather than in formal writing or speech. They often reflect everyday language and can include slang, colloquialisms, or regional expressions. For example, saying "gonna" instead of "going to" is an informal way of speaking. These terms can vary widely based on culture, age, and social groups. While they make communication more relatable and friendly, using informal terms in professional settings, such as business meetings or academic papers, may not be appropriate. Understanding when to use them is key to effective communication.