An
electronic flash meant for
photography in a
studio (or, at least an
indoor) environment.
There are basically two kinds of studio flash systems, the monolight (cheaper) and the generator + heads systems.
A monolight is basically a power transformer, a pack of capacitors, the flash tube and the control electronics all packaged in a brick-shaped enclosure (generally called a torch).
The torch always has some way of attaching it to a stand.
Usually, monolights can be dialed to full power, 1/2, 1/4, and 1/8 (this maps usefully to f-stops).
All monolights have a standard synchro X socket, and most also have an integrated slave sensor, to reduce the cable clutter on the studio floor.
In a generator + heads system, the transformer and capacitors sit on the floor in a big, heavy box, connected to the flash tubes (or "heads") by power cables. A generator can typically power three heads. The big advantage with a generator system is that you can control all your lights from a central location. A secondary advantage is that the heads are generally lighter than monolights, hence easier to move around.
Studio flash systems usually have very little or no automation. You have to set the light power and ratio by yourself, usually after careful measuring with a flashmeter. This means that, with one of those systems, it is almost immaterial what camera you are using: as long as it has a PC synchro socket, it will work.
The real worth of a studio flash system is in the accessories: accessories for filtering and shaping light. The prince of the accessories is probably the softbox. There are also barndoors, snoots and all sorts of other things to bend the light to your liking.