E-liquid is the mixture used in vapor products such as electronic cigarettes. The main ingredients in the e-liquid usually are propylene glycol, glycerin, nicotine, and flavorings.

  The aerosol of electronic cigarettes is generated when the e-liquid reaches a temperature of roughly 100–250 °C within a chamber. The user inhales the aerosol, commonly called vapor, rather than cigarette smoke. The aerosol provides a flavor and feel similar to tobacco smoking... Wikipedia