Right-Hand Rule
Definition
A hand gesture that tells you the direction of magnetic forces and fields — point fingers, curl, thumb gives the answer.
Technical definition
A mnemonic for cross-product directions: for F = qv × B, point fingers along v, curl toward B, thumb gives F (for positive charge). Variants give field direction around a current (thumb = current, curled fingers = field) and induced current directions.
Example
Current flowing toward you in a wire: point your right thumb toward yourself, and your curled fingers show the magnetic field circling counterclockwise.
Common confusion
There are several right-hand rules (force on charge, field around wire, solenoid polarity, Lenz's law) — mixing up which version applies is the classic error. Each answers a different cross-product question.