Parallels RAS Client is a software application used to access virtual desktops and applications delivered by Parallels Remote Application Server (RAS). It enables users to securely connect to their virtual resources from various devices, including Windows PCs, Macs, Linux computers, smartphones, and tablets. The client provides an intuitive interface for launching and interacting with virtual desktops and applications, offering features such as seamless window mode, file transfer capabilities, and multi-monitor support.