Year zero
ISO 8601:2004 (and previously ISO 8601:2000, but not ISO 8601:1988) explicitly uses astronomical year numbering in its date reference systems. Because it also specifies the use of the proleptic Gregorian calendar for all years before 1582, some readers incorrectly assume that a year zero is also included in that proleptic calendar, but it is not used with the BC/AD era. The "basic" format for year 0 is the four-digit form 0000, which equals the historical year 1 BC. Several "expanded" formats are possible: −0000 and +0000, as well as five- and six-digit versions. Earlier years are also negative four-, five- or six-digit years, which have an absolute value one less than the equivalent BC year, hence -0001 = 2 BC. Because only ISO 646 (7-bit ASCII) characters are allowed by ISO 8601, the minus sign is represented by a hyphen-minus.
2000s (decade)
In the English-speaking world, a name for the decade was never universally accepted in the same manner as for decades such as the '80s, the '90s, etc. Orthographically, the decade can be written as the "2000s" or the 00s". Common suggestions for referring to this decade: "2000s", "Two-thousands", "Twenty Hundreds", "Twenty-ohs", "00s" (pronounced "Ohs", "Oh Ohs", "Double Ohs" or "Ooze", "Zeros", "Double Zeros"), "the Aughts", "the Noughties", "the Aughties", "the Oughties". Other suggestions from 45 countries suggest the "double nothings", "zilches", "oh-zone", "oh-something". When the "20–" is dropped, the individual years within the decade are usually referred to as starting with an "oh", such as "oh-seven" to refer to the year 2007. During the decade of the 2000s, it was more common to hear years referred to starting with "two-thousand (and)" rather than "twenty-oh". Starting around the middle of the 2010s, it is becoming more common to refer to the individual years of the decade as "twenty-oh-seven" or "twenty-oh-eight" than it had been during the 2000s, although the "two thousand (and)" pattern is still dominant.