superposition
A qubit's ability to hold a blend of 0 and 1 at the same time, until it is measured.
A bit must be one value at a time. A qubit in superposition carries a weighting of both values at once. When it is measured, it settles to 0 or 1, with odds set by that weighting. A quantum program shapes those weightings so the right answer becomes the likely one. Measuring too early, or any disturbance, destroys the blend.
Think of it as
Like a coin spinning on a table: while it spins it is neither heads nor tails, and only when it lands do you get one answer.
Example
A quantum program is run and every qubit is read at the end. Each qubit gives a plain 0 or 1. The program's skill lies in making the useful pattern of 0s and 1s come up most often.