The Cloudflare Under Attack Mode feature helps mitigate Layer 7 DDoS attacks by enabling additional protections to stop malicious HTTP traffic. When enabled, visitors briefly see an interstitial page while Cloudflare performs additional security checks:
Validated users are allowed to access your website content while suspicious traffic is blocked.
To enable I'm Under Attack mode, see How do I enable I'm Under Attack mode.
Why am I getting a "Checking your Browser before accessing" message before entering a site on Cloudflare?
The "Checking your browser before accessing example.com" page occurs when the site owner has turned on this I'm Under Attack Mode setting. The page will generally go away and grant you access to the site after 5 seconds.