passband signal
modulated signal
Because a modulated signal can encode information in the amplitude, frequency, or phase of the carrier wave, it is
\begin{equation}
s(t) = \alpha(t)cos(2\pi (f_c + f(t))t + \theta(t) + \phi_0)
\end{equation}
Alternatively,
\begin{equation}
s(t) = \Re\{u(t) e^{j2\pi f_c t}\}
\end{equation}
where \(u(t) = s_I(t) + js_Q(t)\).