what is the liquid inside the lighter?

Lighter fluid may refer to:

Butane, a highly flammable, colorless, easily liquefied gas used in gas type Lighters and Butane torches

Naphtha or White gas, a volatile flammable liquid hydrocarbon mixture used in wick type lighters and burners

Charcoal lighter fluid, an aliphatic petroleum solvent used in lighting charcoal in a barbecue grill