A DIN rail is an accessory commonly used in the field of electronics to mount circuit breakers or control apparatuses within equipment racks. They are especially common in Europe. DIN isn't actually an acronym for any sort of electronic jargon; it stands for Deutsches Institut für Normung (German Institute for Standardization).
DIN rails are built to industry standard specifications, meaning any device designed to fit in a DIN rail setup will fit, regardless of who manufactured the device. Even if multiple components from different manufacturers are being used, they will all conform to the DIN rail standard.
The most common DIN rail is of the T35 design. It's a 35 mm wide rail, either 7.5 mm or 15 mm high. The profile of a DIN rail is shaped almost like a top hat, with two lower sides and a raised center. Most of the time, the 7.5 mm DIN rail is used, though in cases where especially heavily objects are to be mounted, the 15 mm version provides some additional stability.
DIN rails are usually manufactured from stainless steel, aluminum or copper, though other basic metals are sometimes used. It is important to be aware of the type of metal you choose for your DIN rail.
Generally, you want the metal of the DIN rail to match the metal of the enclosure. For instance, if you're trying to prevent a damp environment from corroding the metal, an aluminum enclosure might be selected. If a copper DIN rail was then used, it might corrode anyway, defeating the purpose of the aluminum enclosure altogether.
Stainless steel DIN rails are best suited to situations when the DIN rail is expected to secure a significant amount of weight. Stainless steel is also resistant to corrosion – but it's also the most expensive option.
Aluminum DIN rails are best used in damp or humid spaces. Zinc-plated copper or steel DIN rails are the most cost-effective option available. These metals are more prone to corrosion, but the zinc plating helps prevent this. Copper DIN rails are preferred when the DIN rail will be used as a ground.