Iris is the Greek word for "rainbow," and in Greek mythology Iris was the goddess and personification of the rainbow, who served as messenger between the gods and humans. She is often depicted with golden wings, carrying messages from Olympus down to earth along the arc of the rainbow. The flower we call iris was named after her, for the many colours its petals can take.
The name has been used in English since at least the eighteenth century, but its current rise is a contemporary phenomenon. Like Hazel, Willow, and Ivy, Iris belongs to the wave of botanical and natural names rising in the 2010s and 2020s — short, soft, with a single clear meaning that almost any parent can love.
It carries quietly classical credentials (the mythology), modern style (the brevity), and timeless beauty (the flower).
Iris reduces to three in Pythagorean numerology — the number associated with creativity, expression, and joy. A messenger's number for a messenger's name.