Micronutrient are elements which are

Micronutrients are elements that are required by plants in small quantities.
Micronutrients are essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain growth and development.
There are about seven nutrients essential to plant growth and health that are only needed in very small quantities, and these are B, Cl, Cu, Mn, Mo and Zn.