Resistance - That property of a material that impedes the flow of electrical current, reduces voltage and dissipates power in the form of heat in an electrical circuit. The unit of measurement for resistance is the OHM which is defined as the resistance required to maintain an electrical current of one AMP at One Volt.

1 OHM = 1AMP @ 1VOLT

The electrical symbol for resistance is the  Ω or the Greek Letter 'Omega'.

Resistor- The Reference designator for the resistor per ANSI Y32.2 is R

One Thousand Ohms is abbreviated with K as in Kilo-Ohms (10K = 10,000 ohms)

One Million Ohms is abbreviated with M as in Meg-Ohms (100M = 100,000,000 ohms)

Resistors are available in Axial, Radial, Power D-PACK or TO-220, SIP arrays, SMT Chip packages and thick film embedded resistors that are screened or imaged into a printed circuit.  Axial leaded carbon composition resistors come in 1/10W, 1/8W,1/4W, 1/2W, 1W, 2W 5W, 10W sizes... sized for the watts of power they can dissipate without being destroyed by the heat they generate.

Some sources for resistors would be Bourns, Dale, SRT, Rohm, Caddock... there are many.

Resistor Schematic Symbol

Resistor Color Code - A code for determining the value in Ohms of an axial leaded resistor.

See the Graphical Resistance Calculator - http://www.dannyg.com/examples/res2/resistor.htm

Black    = 0

Brown   = 1

Red      = 2

Orange = 3

Yellow  = 4

Green   = 5

Blue     = 6

Violet   = 7

Gray     = 8

White   = 9

None   = 20% Tolerance

Silver   = 10% Tolerance

Gold    = 5% Tolerance

RG cable -  or coax as we know it, was developed by Bell Laboratories during WWII.  Aircraft radio systems that required long-wire antennas, like for example long range bombers, needed a method to route the signal to either the belly or tail mounted long-wire reels without radiating within the fuselage.  Bell Labs developed it and called this new cable Radio Guide or "RG".