Year 81 (LXXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Silva and Pollio (or, less frequently, year 834 Ab urbe condita). The denomination 92 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

"81" (read "Infinity Ichi"; translated as "Infinity 1") is Do As Infinity's twenty-first single, released on June 17, 2009. The band had disbanded in September 2005, but reformed three years later in September 2008. This is the first new single the band released after reforming, and is the first single by the band not to have Dai Nagao on the staff. The single contains four songs, though none are named "81", and this is the first Do As Infinity single not to contain instrumental versions of any song. A music video was produced for "Umareyuku Monotachi e" directed by Kensuke Kawamura.

A priority call is a telephone call that has been assigned some enhanced level of for processing by a telecommunications network such that it may be expected to achieve precedence over other traffic. In any given network, several levels of priority can be assumed to exist.

Telephone numbers in Japan are similar to telephone numbers that are the North American Numbering Plan. However, there are many differences between the North American plan and the Japanese plan.