Euler’s equation is given as  $$dp =  – \rho vdv$$ This equation applies to an incompressible and in-viscid flow where $\rho  = \,{\rm{constant}}$. In a streamline, in between two points 1 and 2, the above Euler equation can be integrated as  $$\int\limits_{{p_1}}^{{p_2}} {dp =  – \rho \int\limits_{{v_1}}^{{v_2}} {vdv} }$$ $${p_2} – {p_1} =  – \rho \left( {\frac{{v_2^2}}{2} – \frac{{v_1^2}}{2}} \right)$$ $$\Rightarrow {p_1} + \frac{1}{2}\rho v_1^2 = {p_2} + \frac{1}{2}\rho v_2^2$$ This can be written as $$p + \frac{1}{2}\rho {v^2} = {\rm{constant}}$$ for a streamline.For an rotational flow the value of constant is changing from streamline to another.For irrotational flow,the constant is same for all streamlines and  $$p + \frac{1}{2}\rho {v^2} = {\rm{constant}}$$ throughout the flow. Physical significance of Bernoulli’s equation is that when the velocity increases, the pressure decreases  and when the velocity decreases, the pressure increases.