Inert and participating electrodes:

If the electrode material is of the type: 'very weak' (as reductor or as oxydator he is nothing), than this electrode will be INERT. The only activity is transporting electrons, but it does not take part in the real redox reaction.
Examples: gold, platinum, graphite.

On the other hand, we use electrodes made of materials that really participate in the redox reaction, for example, in the case of an iron or zincum electrode.
An iron bar can very well serve as an electrode, but will send iron ions into the solution, while electrons remain behind in the barr.
Really, after some time such an electrode will slowly be consumed; it becomes thinner and disappears.

The iron suffers the following half reaction: Fe Fe2++2e-
  1. Fe is the iron of the electrode
  2. The Fe2+ -ions go into the solution to move there freely in the direction of the negative electrode.
  3. The electrons staying behind in the iron electrode will participate in the electron transfer and the electron transport.

A participating (so not inert) electrode always is made of neutral, non noble metals; they serve as reductors, or: they can donate electrons.

non-metals and electrolytes cannot serve as material for electrodes, metals and graphite will do.
a corrosive metal Sodium never is used as electrode in a salt solution