What is a Right Hand Rule?
The right hand rule is a common mnemonic for understanding orientation of axes in 3D space.
One use of the rule is for understanding direction in Physics, specifically Magnetism.
Using the rule, a student can figure out the direction of magnetic fields (B), current (I), charge (Q), and force (F).
There are three variations of the rule and a special case, each with a different purpose.
RHR #1 - Determining the direction of a magnetic field given current
RHR #2 - Determining the direction of force given current and a magnetic field
RHR #3 - Determining the direction of a force given charge and a magnetic field
RHR #4 (unofficial) - Determining the direction of current as a result of a change in magnetic flux
If you want a detailed explanation, visit these links:
Khan Academy
Magnet Academy
Wolfram
Magnetic Flux