could someone tell me the difference between a "short" and "dead short"?
Usually they are the same thing. Though some people use "short" for a short on device/component and a "dead short" as a short of the power in wiring to neutral/ground.

How are these caused, on say an oven
On an electric oven you have 2 power in wires L1 and L2 and a Neutral (return line) which is attached to the frame in a 3 wire hook up. If one of the wires L1 or L2 looses it's insulation or comes loose and touches the frame you have a short and your breaker blows.

how are these detected using a multi meter?
Now some basic electrical. Voltage is like the pressure pushing electrons through the wire, amperage is the number of electrons going through the wire, resistance is the resistance the components have to the flow of electrons.
If you have 0 resistance (a short) (0 ohms) there is nothing to restrict the flow of electrons so they flow at very high current. This blows the breaker which senses the amount of current going through it and opens if the current exceeds the breaker's rating.
As an example of an oven running correctly. If the element runs on 240 volts and the element has 10 ohms of resistance then the current is limited to 24 amps. If a short occurs you get hundreds of amps.

To find a short.
Disconnect the unit from power.
Measure from the L1 to Neutral and L2 to Neutral, they should be higher than 0 ohms.
Note: you may have to turn the dials etc. to the on position since some of the wires are only in circuit/powered when the dial is turned on.

Often on an oven once the covers are removed the short is obvious re burned up wires or arc/weld marks on the frame.

NOTE: An electric oven uses 240 volts which is lethal so care must be taken and unless you know what you are doing always unplug the unit when working on it.

Hope the above helps and makes sense.