Planus is a surname of French origin. People with that name include:
- Marc Planus (born 1982), French footballer
- Pierre Planus (born 1979), French footballer
Planus is a Latin adjective meaning "flat" or "plain". It is part of the binomial name of several species, and of some other combination terms.
- Personal honorific or nickname
- Doctor Planus et utilis, a scholastic accolade awarded to the Franciscan teacher Nicholas of Lyra (c.1270–1349)
- In biology
- Agrypnus planus, a species of click beetle in the genus Agrypnus
- Aneflus planus, a species of beetle in the family Cerambycidae
- Argopatagus planus, a species of sea urchin of the family Macropneustidae
- Blissus planus, a species of true bug in the genus Blissus in the family Blissidae
- Botrylloides planus, a synonym of Botryllus planus
- Botryllus planus, a species of colonial ascidian tunicate in the genus Botryllus in the family Styelidae
- Brachys planus, a species of beetle in the genus Brachys in the family Buprestidae
- Bransatoglis planus, an extinct species of dormouse
- Brochocoleus planus, a species of beetle in the genus Brochocoleus in the family Ommatidae
- Callionymus planus, a species of dragonet native to the shallow Pacific waters off southern Japan
- Camponotus planus, a species of carpenter ant; see List of Camponotus species
- Canthyporus planus, a species of beetle in the genus Canthyporus in the family Dytiscidae
- Carabus perrini planus, a subspecies of beetle in the family Carabidae
- Carabus planus, a synonym of Pheropsophus aequinoctialis, a ground beetle
- Caracara planus, the crested caracara (also known as the carancho), a bird of prey in the family Falconidae
- Catogenus planus, a species of beetle in the genus Catogenus in the family Passandridae
- Cheliferoides planus, a species of spider in the genus Cheliferoides
- Cleptomartus planus, a synonym of Anthracomartus hindi, an extinct species of arachnid in the genus Anthracomartus in the family Anthracomartidae
- Coccophagus planus, a species of chalcid wasp in the genus Coccophagus
- Copodus planus, an extinct species of cartilaginous fish; see List of prehistoric cartilaginous fish genera
- Corax planus, an extinct species of shark in Corax (genus)
- Craspedites planus, an extinct species of ammonoid cephalopod in the genus Craspedites
- Dermestes planus, a species of beetle in the genus Dermestes in the family Dermestidae
- Dicynodon planus, a synonym of Oudenodon bainii, an extinct dicynodont in the genus Oudenodon
- Distichus planus, a species of beetle in the genus Distichus in the family Carabidae
- Epicadus planus, a species of spider in the genus Epicadus in the family Thomisidae; see List of Thomisidae species
- Eucastor planus, an extinct species of beaver found in the Hawthorn Group
- Ferganosuchus planus, the type species of Ferganosuchus, an extinct genus of gavialid crocodilian
- Gonicoelus planus, a species of beetle in the genus Gonicoelus in the family Biphyllidae
- Grynobius planus, a species of beetle in the family Anobiidae
- Heteroscyphus planus, a species of Marchantiophyta (liverwort)
- Hoplobunus planus, a species of harvestman in the family Stygnopsidae
- Hyalodiscus planus, a species of diatom in the genus Hyalodiscus
- Hydroporus planus, a species of water beetle in the genus Hydroporus
- Ischyodus planus, an extinct species of cartilaginous fish in the genus Ischyodus
- Isurus planus, also known as the hook-tooth mako, an extinct mako shark that lived during the Miocene epoch
- Larinus planus, a species of true weevil
- Leptodius planus, a species of crab in the genus Leptodius in the family Xanthidae
- Leptotrachelus planus, a species in the genus Leptotrachelus (beetle) in the family Carabidae
- Lionychus planus, a species of beetle in the genus Lionychus in the family Carabidae
- Metacyclops planus, a species of copepod crustacean in the genus Metacyclops in the family Cyclopidae
- Microcosmus planus, a species of Microcosmus, a genus of tunicates in the family Pyuridae
- Oesyperus planus, a species of beetle in the genus Oesyperus in the family Carabidae
- Pachyscelus planus, a species of beetle in the genus Pachyscelus in the family Buprestidae
- Palaeospheniscus planus, incorrect name for the extinct species of penguin Palaeospheniscus bergi
- Pandanus planus, a synonym of Pandanus tectorius, a species of screwpine
- Penestomus planus, a species of spider in the genus Penestomus
- Philodromus planus, a species of philodromid crab spider in the genus Philodromus in the family Philodromidae; see List of Philodromidae species
- Philophlaeus planus, a species of beetle in the genus Philophlaeus in the family Carabidae
- Polydesmus planus, a species of millipede in the genus Polydesmus
- Protorabus planus, a species of beetle in the subfamily Protorabinae in the family Carabidae
- Psellonus planus, a species of spider in the genus Psellonus in the family Philodromidae; see List of spiders of India
- Pseudaspidites planus, an extinct species of mollusc in the genus Pseudaspidites; see 2012 in molluscan paleontology
- Pseudoparasitus planus, a species of mite in the genus Pseudoparasitus
- Pseudospheniscus planus, incorrect name for the extinct species of penguin Palaeospheniscus bergi
- Pterostichus planus, a species of ground beetle in the genus Pterostichus
- Pyrnus planus, a species of spider in the genus Pyrnus in the family Trochanteriidae; see List of Trochanteriidae species
- Rhipicephalus planus, a species of tick in the genus Rhipicephalus in the family Ixodidae
- Senoculus planus, a species of spider in the genus Senoculus in the family Senoculidae
- Sigaretornus planus, a species in the genus Tornus (gastropod)
- Smerinthus planus, The oriental eyed hawkmoth, a moth of the family Sphingidae
- Sphenodus planus, an extinct species of shark in the genus Sphenodus in the family Orthacodontidae
- Styloniscus planus, a species of woodlouse in the genus Styloniscus
- Syngonanthus planus, a species of plant in the genus Syngonanthus in the family Eriocaulaceae
- Tornus planus, a synonym of Sigaretornus planus
- Trachelas planus, a species of spider in the genus Trachelas in the family Trachelidae; see List of Trachelidae species
- Trochus planus, a synonym of Bembicium nanum, a species of sea snail
- Vetustodermis planus, a soft-bodied middle Cambrian animal, a species in the genus Vetustovermis
- Wilcoxius planus, a species of robber fly (or, assassin fly) in the genus Wilcoxius in the family Asilidae; see List of Asilidae species: W
- Other uses
- Cantus planus, Latin for plainsong (or, plainchant), a body of chants used in the liturgies of the Western Church
- Lichen planus, a disease of the skin and/or mucous membranes that resembles lichen
- Pes planus, a medical term for flat feet (or, fallen arches), a postural deformity in which the arches of the foot collapse