YOLO (You Only Look Once)
Last Updated: July 29, 2026 | By Mihail Sebastian | AI Dictionary
A single-pass object detection algorithm that predicts every bounding box and class label in one network evaluation, fast enough for real-time video.
What is YOLO (You Only Look Once)?
YOLO (You Only Look Once) is an object detection algorithm that predicts all of an image’s bounding boxes and class labels in a single pass through a neural network, fast enough to run on live video. Joseph Redmon and colleagues introduced it in the 2016 paper “You Only Look Once: Unified, Real-Time Object Detection.”
The name is the method. Earlier detectors examined an image region by region, running a model many times per frame; YOLO looks at the whole image once.
How YOLO Works
- Grid division: The image is split into a grid, and each cell is responsible for objects centered inside it.
- Single prediction pass: One convolutional neural network evaluation produces every cell’s bounding boxes, confidence scores, and class probabilities at once.
- Non-max suppression: Overlapping boxes that cover the same object are pruned, keeping only the most confident one.
The single-pass design trades some accuracy on small or crowded objects for speed. Later versions narrowed that gap, and the YOLO name has since been carried forward through successor versions built by different teams.
Example of YOLO
A dashcam collision-warning system runs YOLO on every frame, dozens of times per second. A frame arrives; one network evaluation returns boxes for two cars and a cyclist within tens of milliseconds; the warning logic checks whether any box is growing too fast, which means the object is closing in.
A two-stage detector with better benchmark accuracy would be useless here if its answer arrived after the moment to brake had passed. That trade, accuracy the application can spare in exchange for speed it cannot, is what YOLO was built for.
Related AI terms: Object Detection · Computer Vision · Convolutional Neural Network · Image Recognition
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Mihail Sebastian — Writes about AI governance, regulation, and the technology behind them. Placeholder bio — replace with a real credential line. About