SE stands for Special Edition. This particular Pentax K1000 SE has brown leather vs black and is much more rare than the non-SE, standard models.
The K1000 is a sturdy, incredible 35mm SLR camera and you won't regret this choice if you make it.
A little history of this camera:
The Pentax K1000 (originally marked the Asahi Pentax K1000) is an interchangeable lens, 35 mm film, single-lens reflex (SLR) camera, manufactured by Asahi Optical Co., Ltd. from 1976 to 1997, originally in Japan. The K1000's extraordinary longevity makes it a historically significant camera. The K1000's inexpensive simplicity was a great virtue and earned it an unrivaled popularity as a basic but sturdy workhorse. The Pentax K1000 eventually sold over three million units.
The K1000, introduced in 1976, is the simplest member of Asahi Optical's Pentax K-series 35mm SLRs. The other members are the Pentax K2, KM, and KX, introduced in 1975, and the K2 DMD of 1976. All have the same basic body design, but with differing feature levels, electronics, and controls. The K1000 was the KM with the self-timer, depth of field pre-view and some other features removed to save cost.
It uses a horizontal travel, rubberized silk cloth focal plane shutter with a speed range of 1/1000 second to 1 second, along with Bulb and a flash X-sync of 1/60 second. It is 91.4 millimetres (3.6 inches) tall, 143 mm (5.6 in) wide, and 48 mm (1.9 in) deep, and weighs 620 grams (21.9 ounces). The body was finished in black leather with chrome trim only, although early production Pentax K1000 SE bodies had brown leather with chrome trim.