An outcome in probability is a result of a probability experiment. For example, suppose you toss a coin and H = heads and T = tails.
If the coin lands on heads, the outcome is heads or H.
Suppose you toss the coin twice. The outcome could be TH and TH means that the first time you tossed the coin it landed on tails and the second time it landed on heads.
There is a difference between outcome and possible outcomes.