Everclear is a brand of pure grain alcohol, available in 190 proof (95%) and a less common 151 proof (75.5%) variant. It is produced by the David Sherman Corporation.
Because of its strength it is illegal in many US states, and probably not available outside USA (at least not the 190 proof variant). If Everclear is not sold where you live, plain vodka can be used instead (Everclear is basically a strong form of vodka).
Warning: Can be lethal when used as shots or substituted for water in Jello shooters.