What is orifice (in piping term) and what is the function of orifice in pipes?

An orifice, in general is an opening. I'll just leave it at that.
In piping it is usually a special device used primarily to measure or restrict the flow of a fluid. These are called metering devices.
Here is an example of one type.
A flat metal disc with a known diameter hole is called an orifice plate. It is clamped between special flanges in a section of straight pipe and centered in the pipe so that the fluid flowing through the pipe also passes through the hole and then proceeds on down the pipe.
The two special flanges both have a small hole ( called a tap) drilled thru the sides and on into the pipe opening where the flow is passing. The pressure from the upstream side or "tap" of the orifice plate is compared to the downstream pressure.
Since it is known that pressure drop and velocity are related the measured pressure drop across the known orifice is used in the flow calculation.
Other orifice-type metering devices are used to limit a flow within a certain range. This is common in variable orifice control valves where a tapered plug changes the size of the orifice opening.
Another less common orifice plate application in piping is in flow restriction in the event of a pipeline rupture.
In refrigeraton a common metering device called a capillary. This is actually a smaller diameter tube which does the same as a hole in a flat plate, but does it better.

Industrial application of venturi meter and orifice?

i would be glad if the answer be in detail , and anybody can explain me the application of orifice in the car?

Venturies and Orifice plates are widely used in industries to measure the flow rate of gases and liquids. The working principle is simple and flow is measured using the differential pressure principle.
Even for a wind to blow, there has to be a low pressure and a high pressure. Hence if there is a flow (created naturally or artificially), there is a high pressure upstream and low pressure down stream.
Differential pressure transmitters (DPT's) utilize this principle to measure this pressure difference and transmit the pressure difference signal to a process indicator or controller. This signal is processed by the indicator (meter) and scaled or integrated to engineering parameters like flow rate, totalisation, speed, volume etc., using specific formulas for the particular type of application and medium (gas or fluid).
To summarize, venturies and orifices generate a differential pressure which if integrated with time, can then be used to convert into any engineering parameter like flow rate, quantity, speed etc. and can be used in any industrial, automotive, aeronautical, domestic or just about any field - which comes to imagination.