Is redox potential a valid term?
I mean doesn't every compound has its own different reduction and oxidation potential ? Or its just one potential that can be compared to understand which one will get reduced and which one will get oxidised ?


A compound has neither. You need to specify the half reaction. For example, take an aqueous solution of $\ce{Fe^2+}$ and hydrogen peroxide, among others. What are possible half reactions for $\ce{Fe^2+}$?

$$\ce{Fe^2+ -&gt; Fe^3+ + e-}\tag{1}$$ 
$$\ce{Fe -&gt; Fe^2+ + 2e-}\tag{2}$$

and maybe some more exotic ones. For hydrogen peroxide, you would have e.g.

$$\ce{H2O2 -&gt; O2 + 2e- + 2H+}\tag{3}$$
$$\ce{2H2O -&gt; H2O2 + 2e- + 2H+}\tag{4}$$

Notice that these are all written in the direction of reduction, and are associated with a reduction potential. To see which reactions are feasible, you would compare reduction potentials and come up with a redox reaction combining a half reaction as written with a half reaction (the oxidation half reaction) in the reverse direction. For example, hydrogen peroxide could undergo disproportionation:

$$\ce{2H2O2 -&gt; O2 + 2H2O}$$

This is a slow reaction, but the enzyme catalase (which happens to have an iron(III) bound to its active site) increases the rate substantially, as you can see from the oxygen evolving when you put some hydrogen peroxide on a freshly cut slice of potato.


  Is redox potential a valid term?


Yes, under certain circumstances it makes sense to talk of redox potential as a property of an aqueous solution, similar to discussing its pH. For example, if a biological cell contains glutathione at fairly high concentration in the reduced and oxidized form (abbreviated as GSH and GSSG), this will determine the redox state of other substances in the cell. If a strong oxidation agent is introduced, it will react with GSH. If a strong reduction agent is introduced, it will react with GSSG. Like mainining a pH with a buffer, the redox potential of the cell is maintained through the ratio of GSH and GSSG (and we could call it a redox buffer).

The analogy between pH buffer and redox buffer only goes so far. The biggest difference is in the role of water. While water acts as an acid and base at any pH (i.e. whenever acids and bases are added), it does not undergo reduction and oxidation for many redox reactions in aqueous solution. Any pair of acid and base will react (because water provides the "reservoir" of hydrogen and hydroxide ions). Many pairs of possible oxidizing and reducing agents will not react, even when thermodynamically favored because there is no good mechanism for the electrons to be transferred (a question of kinetics).