the discordian or erisian calendar is an alternative calendar used by some adherents of discordianism. it is specified on page 00034 of the principia discordia.
the discordian year 1 yold is 1166 bc. (elsewhere in the principia discordia, it is mentioned that the curse of greyface occurred in 1166 bc, so this is presumably related to the start-date of the calendar.) as a reference, ad 2020 is 3186 yold (year of our lady of discord). the abbreviation "yold" is not used in the principia, though the phrase "year of our lady of discord" is mentioned once.