Historically, OS referred only to the dating practice starts today of the year change to 1 January from March 25, and some historians still believe this is the best practice.
Also, even beforethe see more sometimes dating sites in to be double dated because different countries began the year on different dates. For instance, the calendar in the British Empire did not immediately change.
For details on the change from Lunisolar calendars, see Adoption of the Gregorian calendar.Yoga For Complete Beginners - 20 Minute Home Yoga Workout!
JapanKoreaand China started using the Gregorian calendar on 1 January, andrespectively. They had used lunisolar calendars previously.