Lenz’s law gives the direction of an induced current as opposing the change that causes it.
Heinrich Lenz formulated the rule in 1834. When magnetic flux through a circuit changes, an induced current appears. The magnetic field produced by that current acts against the change in flux, whether the original field is increasing or decreasing. This direction is represented by the minus sign in Faraday’s law of induction.
For example, moving a magnet toward a conducting loop causes the loop to produce a magnetic field that resists the approach. Pulling the magnet away reverses the induced current so the loop resists the decrease in flux.
Lenz’s law does not mean induced currents always oppose an external magnetic field itself. They oppose the change in magnetic flux. The rule also reflects conservation of energy: if the induced current assisted the change, energy could appear without an input of work.