Colours that sit next to each other on the colour wheel — a harmonious, low-contrast pairing.
Hues within roughly 30–60° of each other on the hue wheel.
Analogous colours can still contrast in lightness or saturation even though their hues are close.
Blue, teal and green form an analogous group.
Analogous pairings are the usual choice when a 'subtle' rather than 'bold' pairing is wanted.