Panicle
A branched flower cluster: a main stem with side branches that each carry several flowers.
A panicle is a raceme that branches. The main stem carries side stems, and each of those carries its own flowers, so the whole cluster is loose and often cone-shaped or cloud-like. Lilac, astilbe and many hydrangeas carry panicles. So do oats, rice and most ornamental grasses. Gypsophila, the tiny white flower sold as baby's breath, is a much-branched airy cluster of this general kind, which is why one stem fills so much space in a bouquet.