Posh means smart and expensive, or upper class in manner. A posh restaurant, a posh accent, posh frock.
It is British and does two jobs: of things it means expensive, and of people it is a class judgement that can be admiring or hostile depending on who is speaking. The story that it stands for port out, starboard home is charming and untrue.
1adjectiveposhSmart and expensive, or upper class in manner.
“They took us to a posh restaurant where the waiters wore white gloves.”
posh is a quality.
The origin is uncertain, possibly from a Romani word meaning half. The port out, starboard home story is a myth.
rom
posh — half
English, today
posh
unknown. Most likely derived from rom posh (“half”), either because posh-kooroona (“half a crown”) (originally a substantial sum of money) was used metaphorically for anything pricey or upper-class, or because posh-houri (“half-penny”) came to refer to money generally. A period slang dictionary defines "posh" as a term used by thieves for "money: generic, but specifically, a halfpenny or other small coin". An example is given from James Payn's The Eavesdropper (1888): "They used such funny terms: 'brads,' and 'dibbs,' and 'mopusses,' and 'posh'... at last it was borne in upon me that they were talking about money."
Etymology from Wiktionary, CC BY-SA