a | c | d | g | n | p

Anode -  The output electrode which collects most of the electrons, usually connected via a "load" to positive HT supply (B+). On a diode or rectifier with a positive output it is the AC in. On a rectifier or diode with earth or AC on the cathode it is the negative output.
- Synonyms: Plate, plate
Cathode -  The source of electrons in the device. if "indirect" then the cathode is tube with an internal insulated heater. A filamentary cathode is a filament heated by voltage across it which acts as the cathode.
- Synonyms: filament
DMM -  Digital Multimeter. Cheap ones have 1M ohm input resistance on all voltage ranges and more expensive models usually 10 M Ohms. The accuracy isn't the visible digits. The last digit can be very misleading. An analogue meter is a different resistance on each DC Voltage scale. The "ohms per volt" applies to the full scale value. Usually much lower input resistance on DC and often on Ohms the "+" lead is negative.
- Synonyms: DVM
Grid -  An intermediate electrode between the Cathode (or Filament on a direct type) and the Anode (Plate). Types of grid include "Control" (g1) which controls the electron flow, "Screen" (g2) which is an electrostatic screen between Anode and Control grid improving RF performance, "Suppressor" (g3) which suppresses secondary emission between the Anode and Screen grid. The Control g1 is usually more negative than Cathode, Screen g2 is usually at a higher voltage than Anode and Suppressor g3 usually at Cathode voltage. Physically the grids can be helical fine wire, a mesh, rods, plates. Rods or Plates need an electron beam.
NOS -  New Old Stock: An item allegedly never used. It could be 5 years old or 80 years old. It could be something not produced for 50 years, or recently, or still in production. A sealed box is no proof. Tested is a more useful indication on older items.
pinch -  Type of seal on a vacuum tube (or low pressure gas filled) that is identical to a the pinched tube with support wires visible inside a regular filament lamp. Smaller types have an outward pinch on the entire glass tube.
pip -  The remains of the small sealed tube used to evacuate air from the tube. It can be visible on the top, or the top cap wire may exit via it. Alternatively it may be "hidden" in the base connector holding the pinch or even in centre of a button base.