An aqueous solution is solution of water of a substance. For example, if you heat sodium chloride until it melts, it is called molten sodium chloride, but if you dissolve sodium chloride in water, it is called aqueous sodium chloride.
Electrolysis of aqueous solution is different from electrolysis of molten electrolyte because an aqueous solution contain more types of ions.

Example: Ions presence in molten sodium chloride are Na⁺ and Cl^–

NaCl → Na⁺ + Cl^–

Ions presence in sodium chloride solution are Na^+,H^+,O^2-and Cl^–

NaCl → Na⁺ + Cl^–

H₂O → 2H⁺ + O^2-

Conclusion: In an aqueous solution, it can be more than 1 positive and negative ions.

When the ions move to the anode and cathode, only 1 negative ion and 1 positive ion will be selected to be discharged, and this is called selective discharge.
There are three main factors that affect the selective discharge in electrolysis:
1. position in the electrochemical series
2. the concentration and
3. the type of electrode