Mixed Reality (MR) is a technology that embeds virtual objects into the real world and allows users to interact with these objects as if they were actually physically present. Unlike augmented reality (AR), where virtual objects are projected onto the real world, mixed reality allows users to be seamlessly immersed in a virtual environment where virtual objects are anchored in the real world.
Microsoft in particular uses the term Mixed Reality to describe its technologies and products, which include both virtual reality (Windows MR headsets) and augmented reality (Hololens).
Microsoft HoloLens is a head-mounted display (HMD) that offers both AR and VR experiences. It projects virtual objects into the real world, allowing users to interact with them while still seeing the real environment. Windows Mixed Reality is a platform developed by Microsoft that allows users to create and enjoy VR and AR experiences on Windows 10 PCs.
Microsoft is also using the term Mixed Reality as part of its strategy to break down the barriers between the physical and digital worlds. I was told by a Hololens developer at an event that Microsoft also uses the term MR to better differentiate itself from competing products. So there's a pinch of clever marketing in there, too. However, Mircosoft has not been very successful with MR products so far. It is rumored that there will no longer be a Hololens 3. Furthermore, Microsoft products that initially ran exclusively on Windows MR products are now also available on Meta headsets like the Quest.
Meta's Mark Zuckerberg also uses the term to describe his latest headset, Quest Pro. These new glasses can enable AR experiences through integrated outward-facing first person cameras.
The term MR is also used in various contexts for AR and VR applications and thus cannot be clearly distinguished from neighboring technologies. Nevertheless, mixed reality implies a close interweaving of virtual and real objects.