Example of Real Time Testing :
On Banking Reservation of Airlines/Railway/..etc.
On Banking: Suppose if you are working on the system and you have entered a/c holder name to get his/her details of bank transactionS and if you gets a blank screen/some other screen which are not related to what you are supposed to get that is an error
That is an error.
On Airlines/Railway/..etc: Suppose you are working on the system surfing to get the information of the Available Airlines/Trains/...etc by entering the times of Arrival/Departure dates with timings and if you get blank screen/some other details which wouldn't be related too what you are supposed to get is also an error.