Today is the first of the two Rosh Chodesh ("Head of the Month") days for the month of Adar I (this year being a leap year there are two months called "Adar" -- Adar I and Adar II).
Special portions are added to the daily prayers: Hallel (Psalms 113-118) is recited -- in its "partial" form -- following the Shacharit morning prayer, and the Yaaleh V'yavo prayer is added to the Amidah and to Grace After Meals; the additional Musaf prayer is said (when Rosh Chodesh is Shabbat, special additions are made to the Shabbat Musaf). Tachnun (confession of sins) and similar prayers are omitted.
Many have the custom to mark Rosh Chodesh with a festive meal and reduced work activity. The latter custom is prevalent amongst women, who have a special affinity with Rosh Chodesh -- the month being the feminine aspect of the Jewish Calendar.
Links: The 29th Day; The Lunar Files
Our souls are in exile within our bodies. Our people is in exile within a foreign world.
And so there are two things we must know:
That this is not our place.
And that hidden treasure lies buried here; for G‑d dwells in darkness.
If we remember only that this is not our place, we may remain strong, we may even shine in the darkness. But what profit will there be from our exile?
And if we remember only that treasure lies here, we will begin to believe that this is our place, and if so, of what use is the treasure?