Explain the concept of conversion and provide examples.

Conversion, also known as zero derivation or functional shift, is a process in word formation where a word changes its grammatical category or part of speech without any changes in its form. In other words, conversion involves using a word in a different grammatical context without adding any affixes or altering its spelling.

Examples of conversion can be found in various parts of speech, such as nouns becoming verbs, verbs becoming nouns, adjectives becoming nouns, and so on. Here are some examples to illustrate the concept:

1. Noun to Verb:
- "Google" (noun) to "to Google" (verb): The noun "Google" refers to the popular search engine, but it can also be used as a verb to mean searching for information on the internet using the Google search engine. For example, "I need to Google that information."

2. Verb to Noun:
- "Run" (verb) to "a run" (noun): The verb "run" refers to the action of moving quickly on foot, but it can also be used as a noun to refer to a period of running. For example, "I went for a run this morning."

3. Adjective to Noun:
- "Green" (adjective) to "the greens" (noun): The adjective "green" describes the color, but it can also be used as a noun to refer to vegetables, especially leafy ones. For example, "I bought some fresh greens from the market."

4. Adjective to Verb:
- "Fast" (adjective) to "to fast" (verb): The adjective "fast" describes something that is quick, but it can also be used as a verb to mean abstaining from food or certain activities for a period of time, usually for religious or health reasons. For example, "During Ramadan, Muslims fast from sunrise to sunset."

5. Verb to Adjective:
- "Clean" (verb) to "clean" (adjective): The verb "clean" refers to the action of removing dirt or making something tidy, but it can also be used as an adjective to describe something that is free from dirt or impurities. For example, "Please make sure your hands are clean before touching the food."

These examples demonstrate how conversion allows words to shift between different parts of speech, expanding the flexibility and versatility of the English language.