Plain English: A remote tower lets air traffic controllers work an airport without being in a tower at that airport. Instead of looking out a window, they watch high-definition camera views and sensor data streamed to a remote operations centre.
Technical: A remote tower replaces the out-the-window view with a panoramic array of HD cameras, pan-tilt-zoom optics, infrared and thermal sensors, microphones, and signal feeds. These are reconstructed on displays with aircraft labels, tracking, and overlays. One facility can serve a single airport or, under separate approvals, several.
Distinct operating modes are safety-cased and approved separately: single-airport remote tower, remote tower centre, sequential and simultaneous multiple operations, contingency, and supplemental/enhanced facilities. Multiple-airport operation is an approved-case capability, not a default.