What does conversion refer to in linguistics?

In linguistics, conversion refers to the process of changing a word's part of speech or function without altering its form. This means that a word can be used as a noun, verb, adjective, etc., without any modification in its spelling or pronunciation. An example of conversion is the word "run," which can function as both a noun (e.g., "I went for a run") and a verb (e.g., "I will run tomorrow"). This linguistic phenomenon showcases the flexibility and adaptability of language, allowing speakers to play with grammatical categories seamlessly.

The other options do not accurately reflect the definition of conversion. For instance, making words obsolete relates to language evolution but doesn't align with the definition of conversion. Combining two words into one describes a different process known as compounding, while using grammatical rules to create sentences pertains to syntax rather than to the specific process of conversion.