Scrapy pipelines are components used to process data extracted by spiders. When a spider extracts data, it passes it to the pipeline for processing. Pipelines can perform various operations, including data cleaning, validation, deduplication, and storage. Scrapy supports multiple pipelines working simultaneously, with each pipeline handling different aspects of the data. The execution order of pipelines can be controlled by setting priorities in the configuration file. Common pipeline uses include saving data to databases, saving data to files, sending data to APIs, validating data integrity, and removing duplicate data. Each method in a pipeline must return a dictionary containing the data or an Item object, or raise a DropItem exception to discard the data. Pipelines can also use the open_spider and close_spider methods to perform initialization and cleanup operations when the spider starts and closes. The use of pipelines separates data processing logic from spider logic, improving code maintainability and reusability.