What does "neologism" refer to?

The term "neologism" specifically refers to the act of inventing a new word or phrase, which is exactly what the correct choice signifies. Neologisms often emerge in the context of cultural or technological advancements, where existing language fails to capture new ideas, phenomena, or products. This process enriches the language, allowing for more precise communication.

Neologisms can occur in various fields, including literature, science, and technology, where new concepts require corresponding vocabulary. For instance, in recent years, terms such as "selfie," "blog," and "crowdfunding" have been coined to reflect new social practices and technologies. The ability to create and adopt neologisms is a significant aspect of linguistic evolution and innovation.

In contrast, the other options pertain to different concepts—common sayings represent established phrases widely recognized over time, the study of old languages refers to historical linguistics, and philosophical concepts relate to ideas in the realm of philosophy. None of these options align with the definition of neologism.