An electrolytic capacitor is a type of capacitor that uses an electrolyte (a conductive liquid or gel) to achieve a larger capacitance per unit volume compared to other types of capacitors. These are polarized capacitors, meaning they have positive (anode) and negative (cathode) terminals and must be connected with the correct polarity in DC circuits.
 
Construction
Anode: Made of aluminum or tantalum foil coated with a thin oxide layer (acts as dielectric).
Electrolyte: Provides cathode connection and enhances capacitance.
Cathode foil: Completes the circuit.
Entire assembly is rolled and sealed in an aluminum can.