の

の nominalizes verbs and phrases, turning them into nouns. This lets you talk about actions as things, or refer to 'the act of doing', 'the thing that ...', or use の as a pronoun substitute for a noun. After nominalized clauses, の can function as the subject or object, and it can be followed by particles or be embedded in longer sentences. In casual speech, の often replaces です/だ in explanations or questions.