Abstract nouns are words that represent ideas, qualities, or conditions that cannot be perceived through the five senses. Unlike concrete nouns, which refer to physical objects like apple or car, abstract nouns encompass concepts such as happiness, freedom, and justice. These nouns express emotions, states of being, or characteristics. Examples of abstract nouns include love, courage, and wisdom. They are often used to convey feelings or attributes that are essential to human experience but cannot be touched or seen. Understanding abstract nouns helps in expressing complex thoughts and emotions in language.