Nu (ν) symbol in LaTeX

You can use the default command \nu to get the Nu symbol in LaTeX. Also, you can use the \upnu command provided by the upgreek package to get a slightly different style of the Nu symbol.

\documentclass{article}
\usepackage{upgreek}

\begin{document}

  $$ \verb|\nu| : \nu $$
  $$ [\nu]=\frac{m^2}{s} $$
  $$ \nu =\frac{\mu}{\rho} $$
  $$ \verb|\upnu| : \upnu $$
  $$ [\upnu]=\frac{m^2}{s} $$
  $$ \upnu =\frac{\mu}{\rho} $$
  
\end{document}

Output:

Get bold Nu symbol in LaTeX

To get the bold Nu symbol or any symbol you can use the \bm{} command provided by the bm package.

\documentclass{article}
\usepackage{upgreek}
\usepackage{bm}

\begin{document}

  $$ \verb|\nu| : \nu $$
  $$  \verb|\bm{\nu}| : \bm{\nu} $$
  $$ \bm{\nu} =\frac{\mu}{\rho} $$
  $$ \verb|\upnu| : \upnu $$
  $$ \bm{\upnu} =\frac{\mu}{\rho} $$
  $$ \verb|\bm{\upnu}| : \bm{\upnu} $$
  
\end{document}

Output: