Certain outcome
The outcome of an event is certain to occur when it will always happen in the event.
For example, suppose you have the bag shown in the picture below with all black marbles in it.
If you pick a marble from the bag without looking, what is the probability that you would pick a black marble?
There are only black marbles in the bag. So, picking a black marble is a certain outcome because the bag only has black marbles in it.
In summary, the probability of outcomes can be anywhere from impossible to certain and in between. The increasing probability of outcomes from an impossible outcome to a certain outcome is shown in the following picture.