Mini-Slot
A transmission duration shorter than a full NR slot (2, 4, or 7 OFDM symbols), used for low-latency URLLC transmissions and unlicensed spectrum access.
A mini-slot is NR's escape hatch from slot-boundary delay. A normal slot is 14 OFDM symbols, and waiting for the next slot boundary to start a transmission adds latency you can't always afford. A mini-slot lets a transmission begin at almost any symbol and run for just 2, 4, or 7 symbols — formally this is type B scheduling — so urgent data goes out immediately rather than queuing for the grid.
This is one of the core enablers of URLLC: shorter transmission units mean shorter transmit time and faster HARQ turnaround, shaving milliseconds off the latency budget. It also matters in unlicensed spectrum (NR-U), where a device that's just won a listen-before-talk contention needs to start transmitting right away instead of idling until the next slot edge, both to grab the channel and to satisfy occupancy rules. The cost is overhead and scheduling complexity — each mini-slot needs its own control and DMRS — so it's used where latency genuinely justifies it, not as the default for bulk traffic.
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