outcome (sample point)
An outcome, also called a sample point, is a single, complete, indivisible result of a random experiment — one particular thing that can happen, described in full. It is one element of the sample space. When you roll a die, getting a 4 is an outcome; when you toss a coin twice, getting heads-then-tails (written HT) is an outcome. Each outcome is the finest-grained answer to the question what happened, leaving nothing further to split.
Think of the sample space as a box and the outcomes as the individual marbles inside it. Run the experiment once and you draw out exactly one marble — exactly one outcome occurs, no more and no fewer. Outcomes are often written with a small Greek omega, so a typical outcome is omega and the whole collection of them is Omega. Because every result the experiment can produce is one of these sample points, the outcomes are the atoms from which everything larger — events, probabilities — gets assembled.
Two cautions help. First, what counts as a single outcome depends on how finely you decided to look: for two dice, 'the pair (3, 5)' is one outcome if you track both dice, while 'the total is 8' is not a single outcome but a bundle of several. Second, an outcome is not the same as an event, even though a one-element event looks almost identical; an outcome is a raw element of the sample space, while an event is a set of outcomes you have grouped together to ask a question about.
Roll two dice and record both faces. The outcome (2, 6) is one sample point; so is (6, 2). The statement 'the dice sum to 8' is not an outcome — it gathers up the five sample points (2,6), (3,5), (4,4), (5,3), (6,2).
A single outcome is one marble in the box; a description like a sum is a handful of marbles, i.e. an event.
Exactly one outcome occurs per run; if a description can be true in several distinct ways, you are looking at an event, not a single outcome.