Short Definition
Accuracy is the fraction of predictions a model gets correct.
Intuition
Accuracy answers a simple question: out of all examples, how many were right?
Technical Definition
Accuracy equals correct predictions divided by total predictions, usually for classification tasks.
Example
If a classifier gets 90 of 100 examples correct, its accuracy is 90 percent.
Common Misunderstandings
Accuracy can be misleading on imbalanced datasets.
High accuracy does not guarantee useful precision or recall.