What is concentration gradient?

In general, a gradient is a rate of change of a quantity with distance (distance being the denominator in the rate). Examples of gradients include altitude (the slope of a hill), temperature (which a well-insulated wall should maintain), and pressure (which causes high winds).

A solution in which the concentration varies over a given distance is referred to as a concentration gradient. This does not imply that the change must be uniform with distance, though it may be.

This could happen if you put salt in a glass and then slowly poured water over it; the dissolved salt would be concentrated at the bottom of the glass and much less concentrated at the top.

Concentration gradient refers to the gradual change in concentration of a solute in a solution over a distance. It drives the movement of particles in processes like diffusion.