The name Summilux is used by Leica and Panasonic Lumix to designate camera lenses that have a maximum aperture of f/1.4. The lens has been in production since 1959 and carries on to the present day.
The name Summilux is a combination of Summum, which is the Latin word for highest, while Lux is for light. The first Summilux was the 50 mm of 1959, followed by a new 50 mm Summilux design in 1961, whose optics remained unchanged until replaced by the 50 mm Summilux-M ASPH of 2004. 
The Summilux lenses have a maximum f-number of f/1.4 or f/1.5. This is one stop lower than Leica's Noctilux lenses, but the Summilux lenses are smaller as a result. Summilux lenses are designed for low-light photography.
The Summilux lenses are less expensive than the Noctilux lenses, which has a smaller f-number. However they are bigger, heavier and more expensive than the Summicron.
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