Definition
Sample space
A sample space is the complete set of all possible outcomes of a chance experiment.
What it means
Before finding a probability, make a “nothing missing” list of what could happen. That full list is the sample space. You can show it with a list, table, grid, or tree diagram, as long as every possible outcome appears once at the level you are using.
Remember it
The whole menu of what can happen—nothing missing, nothing counted twice.
Example
Toss a coin and spin a red-or-blue spinner. Using H for heads, T for tails, R for red, and B for blue, the sample space is {HR, HB, TR, TB}.
Watch for
{HR, HB} is not the sample space because it leaves out both tails outcomes; it is only part of the full set.
Common mix-up
An event is the outcome or group of outcomes you care about. The sample space contains every possible outcome.
Exact meaning
A sample space is the set of every possible outcome of a defined chance experiment. Its outcomes must cover all possibilities without double-counting at the chosen level of detail.