Is $0 $ radians an acute angle? I know that an angle less than $\frac {\pi}{2} $ radians is called acute, but under this definition, is an angle that is $0$ radians also considered acute?
According to mathcaptain, which is a website maintained by the publisher Pearson (which publishes math textbooks), an angle of $0$ is called a "zero" angle, an angle of $\pi$ is called a "straight" angle, and an angle of $2\pi$ is called a "complete" angle.
Since you wrote


  I know that an angle less than $\frac {\pi}{2} $ radians is called acute


then obviously an angle of zero radians is acute, simply because $0&lt;\frac {\pi}{2}$.