In the imperative, an exhortation used as a departing salutation.
From keep + it + real.
keep up
To continue with (work, etc).
keep an eye on
To watch and pay attention to, in case of misbehaviour or mishap.
keep quiet
To refrain from talking about something; to keep a secret.
keep on
To persist or continue.
keep someone posted
To inform (someone) regularly of the latest developments.
keep up appearances
To artificially maintain an outward sign of normality; to maintain an …