Reduction refers to a gain of electrons. A specie is said to be reduced when it gains electrons or when it experiences a decrease in oxidation number. The both sentences above can be clearly seen when inspecting a reduction half equation.
Consider the redox reaction half equation;
Fe3+ + 3e– ------>Fe
We can see that Fe^3+ accepted three electrons, the oxidation number of iron thereby decreased from +3 to zero from left to right. This implies that the Fe^3+ was actually reduced according to the equation shown.
