We are given the differential equation:
\[
y^2 \, dx + (3xy - 1) \, dy = 0
\]
Step 1: Check if the equation is linear.
A linear differential equation must be of the form:
\[
A(x) \frac{dy}{dx} + B(x) y = C(x)
\]
In this case, the equation involves terms like \( y^2 \) and \( 3xy \), which are nonlinear terms. Therefore, this is not a linear equation.
Step 2: Check if the equation is homogeneous.
A homogeneous differential equation is one in which all terms are of the same degree. This equation is not homogeneous either because it involves \( y^2 \) and \( 3xy \), which are not of the same degree.
Thus, the equation is not linear and not homogeneous.
Thus, the correct answer is:
\[
\boxed{\text{not a linear equation}}
\]