A soft, pale colour that still has a hint of colour rather than reading as pure white.
Colourwise classifies a colour as pastel when HSL lightness is high (≥70%) and HSV saturation is low-to-moderate (8–45%) — pale but not washed all the way to neutral.
Not every pale colour is a pastel — a pale but strongly saturated yellow reads as 'light and vivid', not pastel.
Baby blue and mint are pastels.
Pastel palettes are a recurring, distinct design trend from muted or jewel-tone palettes.