The heat change accompanying the reaction $2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}(\downarrow ),\mathrm{\Delta H}=-136\mathrm{K}.\mathrm{Cal}$ is called

$2{\mathrm{H}}_{2\left(\mathrm{g}\right)}+{\mathrm{O}}_{2\left(\mathrm{g}\right)}\to 2{\mathrm{H}}_2{\mathrm{O}}_{\left(l\right)},\mathrm{\Delta H}=-136\mathrm{Kcal}$

Here water is formed from hydrogen and oxygen hence, it is called formation. The heat released is called heat of formation.