signal processing - Difference between bit rate and baud rate?

Everyone seems to have different definitions everywhere I look.

According to my lecturer:

$R_{bit} = \frac{bits}{time}$

$R_{baud} = \frac{data}{time}$

According to manufacturers :

$R_{bit} = \frac{data}{time}$

$R_{baud} = \frac{bits}{time}$

Which is the correct one?