what is hysteresis curve explain briefly with the help of diagram.

Dear Student,
Hysteresis in simple words means 'lagging behind'.  The lagging of an effect behind its cause.

Hysteresis is found in many systems such as elastic systems, magnetism, etc.

Remember that you have studied hysteresis in stress and strain curve in 11th.  The strain lags behind stress when you stretch and compress an elastic material. Such hysteresis is also found when you magnetize a material in alternating directions.

When a magnetic material is exposed to magnetizing field in one direction, it's electronic moments align in the direction of the magnetic field. But when the magnetizing field is removed. The substance does not lose its total magnetism in the reverse way retracing its original path. There is a residual magnetism left. So it follows a different path.  In this way a loop is formed between magnetizing field and magnetization. Such a loop is called hysteresis.

Regards