In short, the secretaire en portefeuille is much like a Fall front desk which would have been reduced in depth to a bare minimum. Like the Fall front desk and the Secretary desk the secretaire en portefeuille's desktop lifts up to cover internal areas and must thus be cleared of all work before closing up. By its mobile nature and its relatively light weight it was sometimes used as a Fire screen desk.
Its name comes from the French word for wallet: Portefeuille. This is probably because it has the same proportions as many kinds of wallets and it opens up a bit like some of them.
Modern day cabinet makers and furniture designers have sometimes created contemporary versions of the secretaire en portefeuille, eschewing the florid designs of the antique ones.
See also the list of desk forms and types.