Cilium

A cilium (plural cilia) is an organelle found in eukaryotic cells. Cilia are thin, tail-like projections extending approximately 5–10 micrometers outwards from the cell body.
There are two types of cilia: motile cilia, which constantly beat in a single direction, and non-motile cilia, which typically serve as sensory organelles. Along with flagella, they make up a group of organelles known as undulipodia.