Definition: Continuous crawl is a content crawling mechanism in SharePoint that provides the most recent content in search results compared to Full or incremental crawl.  

Some Points:

• By default, continuous crawl runs every 15 mins
• Continuous crawl works only with content source type: SharePoint Sites
• Multiple continuous crawls can perform simultaneously. So Even if the existing crawl is scanning a large update, another continuous crawl can start at a defined time and perform scan on rest of the updates.
• Once the continuous crawl is enabled, you cannot stop or pause it, you can only disable the crawl.
• You can change the continuous crawl interval only using Microsoft Power Shell.