The Third Sunday of Lent is not a special feast and would simply be called in Latin "Dominica III Quadragesimae."
Septuagesima Sunday
Septuagesima
gaudete sunday, in English, "let us rejoice"
Palm Sunday.
It's called Laetare Sunday (or sometimes Rose Sunday or Refreshment Sunday). "Laetare" means rejoice in Latin. It's the idea that we're half-way through Lent and so we can rejoice a bit that there's alight at the end of the tunnel. "The passage from Isaiah continues, "rejoice with joy, you that have been in sorrow," and on Laetare Sunday, the purple vestments and altar cloths of Lent are set aside, and rose ones are used instead. Flowers, which are normally forbidden during Lent, may be placed on the altar. Traditionally, the organ was never played during Lent, except on Laetare Sunday." from (link below)
Is Mothering Sunday what you are looking for?
The holiday equivalent to Mother's Day in England is called "Mothering Sunday." It is celebrated on the fourth Sunday of Lent, which usually falls in March.
"Some systems name the candle as follows: Candle 1. Hope (purple) Candle 2. Peace (purple) Candle 3. Joy (rose; the corresponding Sunday is "Gaudete Sunday") Candle 4. Love (purple) Candle 5. Christ (white)"
it is mothering Sunday on the 3rd April however because it is mothering Sunday it changes every year!
tertius
There are four Advent candles, three are purple and one is pink. The order of lighting the candles is Purple, Purple, Pink. Purple.The third Sunday of Advent is Gaudete Sunday from the Latin word "rejoice." Gaudete Sunday anticipates the joy of the Christmas celebration, so its color is a mixture of Advent purple and Christmas white
In the Roman Catholic Church, before 1960 the Fifth Sunday of Lent was called Passion Sunday because the (lengthy) Passion of the Lord was read at Mass as the Gospel reading. In 1960, Blessed Pope John XXIII changed the name of Passion Sunday to "First Sunday of Passion-tide," to conform to what Pope Pius XII had done earlier--he had changed the name of Palm Sunday to "Second Sunday of Passion-tide, or Palm Sunday." That lasted until 1969 when Pope Paul VI abolished Passion-tide (as a sort of sub-season of Lent), so as of right now the Sunday before Palm Sunday is officially known as the Fifth Sunday of Lent. But--I suspect many people would know what you are talking about when you say "Passion Sunday", particularly old-fashioned or Traditional Roman Catholics and very high-church Episcopalians
It is commonly known as "Ash Wednesday", so named as the Faithful receive ashes on their foreheads. The ashes, which are a sacramental in the Catholic Church, serve as a reminder that we are mortal and death is certain. With this consideration, it is hoped that the Faithful will give a good effort at sanctifying themselves through Lent, not only to be ready for Easter, but that they be ready for death when it comes.