- (idiomatic, UK) (of a person) in reality; in fact; when it comes down to it. (of a topic) plainly; in plain English; at its most basic level.
- Who is Nelson Mandela when he's at home?
- Feng Shui? What on earth is that when it's at home?
This phrase is an intensifier used to communicate the fact that one knows nothing about a particular person or subject, (Haemoglobin? What in blazes is that when it's at home?), effecting a self-conscious cutesy ignorance that sometimes also carries a humorous irony, depending on context. It often implies derision for the subject, or some erudite, esoteric, overly-technical, or overly-political word used in the company of the speaker.