This is a Jewish leap year. A regular Jewish year is anywhere from 353-355 days. On average it has 11 fewer days than a Gregorian year. Therefore, our sages, in their infinite wisdom, added a leap month 7 out of every 19 years. We are currently in the 6th year of the 19 year cycle, when a leap month is added, making the year anywhere from 383-385 days. The month is added because we are commanded שמור את חדש האביב ועשית פסח לי-ה-ו-ה אלקיך “Observe the month of Aviv and make a Passover for Adonai your God.” While Aviv was the original name for the month of Nissan, it later came to mean spring, and Passover became associated with spring. Hence when Passover is getting to early (before spring) a leap month is added.
Which is the leap month? Most sources say that Adar Rishon, the first Adar, but I believe it is Adar Sheni, the second Adar, as one would not have known s/he needs to intercalate a year until that point in time. The reason most believe that the leap month is Adar Rishon is because Purim is pushed to Adar Sheni. However, that is done because of the connection between Purim and Passover: we are commanded to start (re) learning the Passover laws thirty days after Passover-right after Purim. Thus Purim needs to remain thirty days before Passover and is pushed to Adar Sheni.
A common question I am asked is when someone has a loved one who passed away in Adar in a non-leap year when should his/her Yahrzeit be observed in a leap year. Most authorities say it should be observed in Adar Rishon. That is why the only Yahrzeits that will be listed in Adar Sheni are those for someone who passed away in Adar Sheni during a leap year. Some have the custom of observing the Yahrzeit in both Adar Rishon and Adar Sheni.
The laws surrounding two months of Adar are confusing yet the truth is there are only two practical applications. First, Purim is pushed one month later so that it remains 30 days before Passover. The 14th of Adar Rishon is called Purim Katan, “little Purim,” yet nothing major ritually changes as a result of it. Second, if you have a Yahrzeit in Adar, you can observe it in Adar Rishon or in both Adar Rishon and Adar Sheni.
We are commanded מכנכנס אדר מרבין בשמחה, “when the month of Adar arrives, our joy increases.” My family and I hope that you only experience joy during both months of Adar in 5782.
 Deuteronomy 16:1
 Shulchan Aruch Laws of Passover Siman 429 Seif 1.
 Mishnah Taanit Chapter 4 Mishnah 6