An RDP-accessible system is a host that can be reached over Remote Desktop Protocol, usually on TCP port 3389. It lets administrators log in remotely with a graphical desktop, but if the service is exposed to the internet it becomes a high-value target for attackers.
In cyber security, RDP exposure matters because it can be probed continuously for weak passwords, stolen credentials, misconfigurations, or vulnerabilities in the remote access path. Once attackers gain an RDP foothold, they may install tools, move laterally, steal data, or deploy ransomware. Defenders reduce risk by limiting internet exposure, using VPNs or bastions, enforcing multifactor authentication, patching systems, monitoring logins, and segmenting networks so one reachable host does not become a route into the rest of the environment.