Sister seasons
The two seasons on either side of yours on the color wheel, close enough to borrow colors from.
Sister seasons are the two neighbouring seasons on either side of a given season on the twelve-season color wheel, the ones it flows into and shares one characteristic with. The term is used in two overlapping ways across the industry: some sources, including theconceptwardrobe's season guides, use sister seasons specifically for these flow neighbours, the palettes a borderline person can safely borrow from; others use it more loosely for any season that shares the same dominant characteristic, for example True Spring and True Autumn, which are both dominant-warm despite sitting on opposite sides of the wheel. This site follows the flow-neighbour definition: each season's sisters are the two seasons immediately next to it in the circle Bright Spring, True Spring, Light Spring, Light Summer, True Summer, Soft Summer, Soft Autumn, True Autumn, Deep Autumn, Deep Winter, True Winter, Bright Winter, back to Bright Spring.
Why it matters
Knowing your sister seasons matters most when a result is close, because their palettes are the safest place to borrow a few extra colors from without straying into shades that would genuinely clash with the rest of your natural coloring.