What is the definition of the word impedence?

The Word "Impedance" is much over used, often to mean "resistance". The proper meaning of the Word means the total impedance of a circuit, including the resistive, capacitive, and inductive components. It is always frequency dependant, so that there are standard practices as to the frequency used to measure it.

For example, a general purpose loudspeaker may be specified as having 8 ohms impedance. This takes account of the resistive, inductive, and capacitive components, usually at 1000 Hz. The antenna input to a TV set is usually 75 ohms (or maybe 50 ohms!), measured at some point in the middle of it's frequency range. It is always good to make sure that the antenna and feeder co-ax has the same characteristic impedance.