Magento 2 cache clean vs cache flush?

php bin/magento cache:flush

Flushing a cache type purges the cache storage, which might affect other processes applications that are using the same storage.

php bin/magento cache:clean

Cleaning a cache type deletes all items from enabled Magento cache types only. In other words, this option does not affect other processes or applications because it cleans only the cache that Magento uses.

Reference: DevDocs Manage the cache