2e-8 means?

If it is a calculator output it probably means

$$2e-8=2*10^{-8}$$

otherwise maybe it means

$${\mathtt{2}}{\mathtt{\,\times\,}}{{\mathtt{e}}}^{-{\mathtt{8}}} = {\mathtt{0.000\: \!670\: \!925\: \!255\: \!805}}$$