Capacitor

Both CEDs open the topic with the same sentence: a parallel-plate capacitor consists of two separated parallel conducting surfaces that can hold equal amounts of charge with opposite signs (10.6.A.1 in AP Physics 2, 10.3.A.1 in AP Physics C: E&M). Equal and opposite matters. The net charge on a charged capacitor is zero, and the $Q$ in every capacitor equation is the magnitude on one plate.

The device against its property: this entry is the component, and capacitance is the ratio $C = Q/\Delta V$ that the component has. Both sheets print that ratio and the parallel-plate geometry $C = \kappa \varepsilon_0 A / d$.

How much a capacitor you are allowed to analyse differs by course, and this is the one place the two CEDs part. The AP Physics 2 boundary statement restricts analysis and description to parallel-plate capacitors, with edge effects ignored unless explicitly stated. AP Physics C: E&M expects quantitative analysis of three shapes: parallel-plate, concentric spherical, and coaxial cylindrical capacitors.

Both sheets add a convention that removes a variable before you start: capacitors are air-filled, with dielectric constant $\kappa = 1.0$, unless a question inserts a dielectric.

On a schematic a capacitor is two short parallel lines. In a circuit it starts as a wire and ends as a break, which is the behaviour the RC circuit page covers, and the energy it holds has its own entry.