Especially pertaining to animal bodies indicating a top, a bottom, a front, a back, and a distinctive left as well as right.
Most animals are bilaterally symmetrical, moving within environments in a head-first orientation. Note though that humans, because we are upright, have a front that on other bilaterally symmetrical animals is a bottom and a back that on other bilaterally symmetrical animals is their top.
Bilateral symmetry is a characteristic of all except phylum Porifera, phylum Cnidaria, and phylum phylum Ctenophora. Bilaterally symmetrical animals are also triploblastic and can collectively be described as members of the Bilateria.
Note that members of phylum Echinodermata display a bilateral symmetry as but much less so as adults. Still, echinoderms are considered to be a members of the Bilateria.