The Apple Macintosh SE was launched in 1987 at same time as the Macintosh II. It was an enhanced version of the Macintosh 128 and the Macintosh Plus. It had almost the same specifications as the latter, and unlike the Mac plus, it had an extension slot (which was not compatible with the NUBUS slots of the Macintosh II).
A little trivia: the ROM used only 89 KB of the available 256 KB. So to fill the chip, Apple put the photos of the development team into the ROM. To see these photos, press the debug button then type: G 41D89A.
The Mac 128, the 512k, the 512KE (same but with an 800K floppy drive), and the SE have the signatures of their developers molded as engravings on the inside of the case at the rear.
More information from Luca Rescigno:
The Mac SE had a few different configurations that aren't listed. Originally, there was a dual 800kb floppy configuration or you could replace one of the floppies with a hard disk for extra money. A couple years later it was replaced with the SE FDHD (Floppy Disk High Density) which had a 1.4 MB "superdrive" and a 40 MB hard disk standard. Also, some people have managed to mount an internal hard drive in a dual-floppy SE. There's just barely enough room inside the case. One person even managed to replace both 800k floppies with salvaged 1.4 MB floppies, and they had to replace the ROM chips as well so it would recognize them. Finally, all SEs I've looked inside (including an FDHD) have two floppy controllers on the motherboard and one SCSI connector, so you can theoretically put dual floppies in a newer model.