After experiencing questions from RCIA catechumens and candidates on this topic, I decided to write a short description of the specialized garments used in Catholic liturgical celebrations, as a reference for people who are interested in - but unfamiliar with - the subject.
More information about vestments - both liturgical and non-liturgical - in Catholicism can be found at http://landru.i-link-2.net/shnyves/vestments.htm.
The Alb
The alb is the liturgical garment (or “vestment”) which is proper to all the baptized. It is, in fact, the baptismal garment. From the Rite of Baptism:
{Name} you have become a new creation, and have clothed yourself in Christ. See in this white garment the outward sign of your Christian dignity. With your family and friends to help you by word and example, bring that dignity unstained into the everlasting life of heaven.
Needless to say, the alb is always white in color. It should be long enough to completely cover the “street clothes” that the wearer has underneath (i.e. reaches the floor). Since every baptized Christian may wear this garment by right, you will often see it worn by the altar servers.
Some albs are designed to be worn with a cincture (a rope used as a belt) while others are not. “Monastic”-style albs have a cowl (a hood), while standard albs do not. Ordained ministers wear the alb beneath their other liturgical garments.
A variant on the alb is the surplice, which is also a white garment. Unlike an alb, however, a surplice is not long enough to reach the ground. Instead, it is designed to be worn over a cassock (a long, black robe that may be worn by priests at any time). When I was a boy, altar servers work a cassock and surplice, rather than an alb as they do today.
The Stole
The stole is the liturgical garment proper to all ordained ministers when they preside or assist at any of the sacraments. Deacons wear the stole over their left shoulder (and joining at the right hip) much like a sash. Priests and bishops wear the stole around their necks (resting on both shoulders) with each end hanging down in front.
The Dalmatic
When a deacon assists at Mass, he may wear a dalmatic. Derived from the body-shirts which were the everyday attire of men in the Roman Empire, a dalmatic is a sleeved garment which is worn over the alb. It is the garment proper to a deacon, although bishops have the option of wearing it in addition to a chasuble at Mass.
The Chasuble
In addition to wearing an alb and stole, as he does at all liturgical functions, a priest will also wear a chasuble when presiding at Mass. A chasuble is a sleeveless garment worn over the head and resting on the shoulders (much like a poncho). It is the vestment proper to the Order of Presbyters (priests), although bishops also wear it at Mass.
The Miter
In addition to wearing a chasuble when presiding at Mass, a bishop will, at various times during the Mass, wear a miter. The miter, which is the vestment proper to a bishop, takes the form in the Western church of a tall pointed hat with peaks in front and back. It takes its name from the official headdress of the ancient high priest in Judaism. (See Exodus 28:36-39.)
Liturgical Colors
The color of vestments is determined by the particular feast or season the Church is observing. For seasons, Ordinary Time is observed by the use of green vestments. Advent and Lent are observed by the use of violet vestments, and Christmas and Easter are indicated by the use of white.
Red vestments are word at feasts in honor of the Holy Spirit, the Apostles, or saints who were martyred. Feasts of Our Lord, Our Lady, and certain other saints are indicated by the use of white garments. At funerals, the priest may wear white, violet, or (exceedingly rarely) black vestments.