The PlayStation Multitap is a peripheral for the PlayStation. It is an adapter that can be used to plug in up to four controllers and memory cards at the same time in a single controller port. With a second multitap, up to eight controllers and memory cards can be plugged at once.
The PlayStation Multitap was originally available in gray (SCPH-1070 U) to match the original console's color, however it was later re-released in white as well (SCPH-1070 UH) to match the colors of the later PS one redesign. There was also a smaller version (SCPH-111). All three versions are compatible with the original PlayStation and the PS one, as well as all models of the PlayStation 2 prior to the SCPH-70000 series. Both versions of SCPH-1070 will only function with original PlayStation games, while multiplayer PS2 games required a separate multitap, the SCPH-10090. PlayStation 2 consoles after the SCPH-70000 series require the SCPH-70120 multitap, which is compatible with both PS and PS2 software.
Source: Wikipedia, "[en.wikipedia.org/wiki/PlayStation_Multitap PlayStation Multitap]", available under the CC-BY-SA License.