What is a gradient?

Answer 1

It is the difference in concentration (molecules of a solute per volume of solution) between two locations. Because of the motion of molecules, they are said to diffuse (move, spread) from an area of greater concentration to an area of lesser concentration. Some molecules are always moving in the opposite direction, but the overall trend is "down" the gradient until equilibrium is established between the two regions. And, generally, the larger the gradient or difference, the faster the rate of the diffusion.

Answer 2

In really simple terms (in common usage) the word gradient is used to describe how steep a hill is. However in more technical terms it is a mathematical term which describes the rate at which something changes (be it a slope, like our example of the hill above or more complex things). For a more detailed description of it's mathematical usage, see below:

A gradient describes how fast something changes. For example, the gradient of a curve would be the slope. But gradient can also apply to things like temperature, which don't have a slope.

Gradient- The space rate of decrease of a function. The gradient of a function in three space dimensions is the vector normal to surfaces of constant value of the function and directed toward decreasing values, with magnitude equal to the rate of decrease of the function in this direction.