spikelet n : a small spike (as the inflorescence on grasses and sedges)

A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne towards the base and new flowers are produced as the shoot grows. A plant that flowers on a showy raceme may telegraph the fact in its scientific name, e.g. Cimicifuga racemosa.

A spike is a type of raceme in which individual flowers are sessile (that is, lack pedicels). The term spikelet can refer to a small spike, although it is primarily used to refer to the ultimate flower cluster unit in the grasses (Family Poaceae), in which case the stalk supporting the cluster becomes the pedicel. A spikelet comprises one or more florets enclosed by two glumes (bracts), and is not a raceme.

A spadix is a form of spike in which the florets are densely crowded along the axis.