In layman's terms, an electrochemical gradient is a substance that contributes to cell exchange of proteins and lipids through a cell membrane. It stands to reason that positive- charged ions or molecules will behave in much the same manner as electrons behave in producing electricity. Where a negative situation exists, positive substances will rush in to fill the gap. At this point the situation returns to a neutral state until the negative situation builds up again. This process is what happens to move the necessary water and nutrients from cell to cell.
What factors contribute to the exchange? I quote the following from http://en.wikipedia.org/wiki/Electrochemical_gradient under the subheading Ion Gradients:
1) The difference in the concentration of the solute between the two sides of the membrane
2) The charge or "valence" of the solute molecule
3) The difference in voltage between the two sides of the membrane
Not only is the process carried on in an electrical sense, but the exchange seems to be chemically and biologically produced as well.
A chemist would have an elaborate array of formulas, difficult terms and processes, and present it in a much more effective method than I have here, but for those of us with simpler brains and understandings, this explanation will suffice!