Continuous Crawl in SharePoint 2013

The "Continuous Crawl" is a type of crawl that aims to maintain the index as current as possible. Its operation is simple: once activated, it will launch the crawl at regular intervals. The major difference with incremental crawl is that the crawl can run in parallel, and does not expect that the crawl is completed prior to launch.

Important Points:

• "Continuous Crawl" is only available for sources of content type "SharePoint Sites"
• By default, a new crawl is run every 15 minutes, but the SharePoint administrator can change this interval using the PowerShell cmdlet Set-SPEnterpriseSearchCrawlContentSource,
• Once started, a "Continuous Crawl" can’t be paused or stopped, you can just disable it.

Assume a crawl starts and will take at least 50 minutes,

• After 10 minutes of crawling an item already crawled is hereby amended, and requires a new crawl.
• Crawl "BETA" is launched,
• The crawl "BETA" starts in (15-10) minutes,
• Therefore this item will not need to wait 5 minutes (instead of 50 minutes) to be integrated into the index.

Read more at the below link:
Source: Gokan Ozcifci; https://www.nothingbutsharepoint.com/sites/itpro/Pages/What-is-Continuous-Crawl-in-SharePoint-2013.aspx