The stroller, also known as a Stresemann, a director, or simply black lounge is a form of men's semi-formal daytime dress comprising a single- or double-breasted coat (grey or black), grey striped or checked formal trousers, a necktie (grey or silver), and a waistcoat (dove grey, funeral black, or buff). This makes it largely identical to the formal morning dress from which it is derived, with the exchange of a suit jacket for a morning coat, and the almost exclusive use of a necktie and turndown collar. The correct hat is a bowler, boater hat or Homburg.
For a semi-formal day wedding, the groom dresses in a dark-grey coat with a dove-grey or buff waistcoat; for a funeral, the mourner wears a matching black coat and waistcoat. Traditionally, in the Continent and the Commonwealth, morning dress is worn to formal day events; the stroller in the U.S. (The stroller is the daytime equivalent of the semi-formal evening dress dinner jacket or tuxedo (black tie); morning dress is the daytime equivalent of evening formal dress (white tie).) The recent trend in weddings of ambiguous formality in the United States has led to a sharp decline in the use of either formality.
The term stroller is only used in the US and is unknown in the UK, where, though the garment itself saw a limited period of popularity, was simply called black lounge. Because black was then reserved for formalwear, it was unknown as a colour for lounge suits, so the term was unambiguous. In the UK this mode of dress is now extremely unusual, though some Masonic Lodges which meet during the day rather than (as is more common) in the evening do continue to specify it as their dress code. But this could be because the Masonic Lodges emulate their meetings as celebrated at noon so that even an evening meeting must be attended in the daytime dress. It also still is worn within the legal profession, especially by barristers, indeed the striped trousers are in some circles referred to as "barrister trousers".