Exactly what it says on the tin. I have a Sound Blaster X-Fi Xtreme Audio Notebook sound card and I was measuring its output frequency using frequency counter connected to the card's output. Frequency was generated using a program called FrequencyGenerator.
This article contains information about Cathodic Protection. Cathodic Protection is an electrochemical means of corrosion control in which the oxidation reaction in a galvanic cell is concentrated at the anode and suppresses corrosion of the cathode in the same cell. Figure 1 shows a simple cathodic protection system.
Cathode ray. A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil. Cathode rays are normally invisible; in this tube enough residual gas has been left that the gas atoms glow from fluorescence when struck by the fast moving electrons. Cathode rays (also called an electron beam or e-beam) are streams of electrons observed in vacuum tubes.