SQL and NoSQL are databases used to store data, but they differ in data storage, schema, scalability, queries, ACID compliance, and suitability for fast-paced operations. SQL databases have structured storage with rigid schemas, while NoSQL databases allow free-flowing, dynamic data. SQL is better for complex querying and ACID compliance, while NoSQL offers greater flexibility. Both have their uses based on specific business needs and environments. Choosing the ideal database depends on the level of definition and requirements of the environment.