Whether a state is pleasant or unpleasant. The first of the three axes a feeling is located on, and the one most often mistaken for the whole.
Latin valentia (strength, capacity), from valere (to be strong), named in modern usage a capacity to combine or the pleasant or unpleasant pull of a feeling.
Whether a state feels pleasant or unpleasant, the first of the axes a feeling is placed on and, too often, mistaken for the whole of it.