7. The equation $\left\{\begin{array}{l}x=\frac{1}{2}\left(e^{t}+e^{-t}\right) \cos \theta, \\ y=\frac{1}{2}\left(e^{t}-e^{-t}\right) \sin \theta\end{array}\right.$ where $\theta$ is a constant $\left(\theta \neq \frac{n}{2} \pi, n \in \mathbf{Z}\right), t$ is a parameter, then the shape of the figure it represents is . $\qquad$
7. Hyperbola Hint, converting the equation to a standard form is $\frac{x^{2}}{\cos ^{2} \theta}-\frac{y^{2}}{\sin ^{2} \theta}=1$.