Ground plane
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In electrical engineering, a ground plane is an electrically conductive surface, usually connected to electrical ground.
The large light-green areas on this printed circuit board are the ground plane
Decoupling capacitor
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In electronics, a decoupling capacitor is a capacitor used to decouple one part of a circuit from another. Noise caused by other circuit elements is shunted through the capacitor, reducing its effect on the rest of the circuit. For higher frequencies, an alternative name is bypass capacitor as it is used to bypass the power supply or other high-impedance component of a circuit.
Capacitor packages: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. Major scale divisions are cm.
Impedance curves of aluminum electrolytic capacitors (solid lines) and polymer capacitors (dashed lines)
1980s Commodore 64 main board. Most of the "orange" round disc parts are decoupling capacitors.
1980s Cromemco XXU, a Motorola 68020 processor S-100 bus card. The axial parts between the ICs are decoupling capacitors.