In the hierarchy of the Catholic Church, you have the Pope at the top (well, after God), cardinals, bishops, priests, and then deacons. Catholics recognize two types of deacons:
Permanent deacons are men ordained to an office in the Catholic Church who normally have no intention or desire of becoming priests. He can be single or married. If the latter, he must be married before being ordained a deacon. If his wife dies before him, he may be ordained a priest if the bishop permits and approves.
Permanent deacons, especially those who are married, have secular jobs to support their families and also help the local pastor by visiting the sick, teaching the faith, counseling couples and individuals, working on parish committees and councils, and giving advice to the pastor.
Transitional deacons are seminarians, students in the last phase of training for the Catholic priesthood. After being a deacon for a year, they’re ordained a priest by the bishop.
Deacons can baptize, witness marriages, perform funeral and burial services outside of Mass, distribute Holy Communion, preach the homily (which is the sermon given after the Gospel at Mass), and are obligated to pray the Divine Office (Breviary) each day. (The Divine Office, Breviary, or Liturgy of the Hours are all the same thing. These are the 150 Psalms and Scriptural readings from the Old and New Testament that every deacon, priest, and bishop must pray every day and a few times during each day.) This way, in addition to the biblical readings at daily Mass, the cleric is also exposed to more Sacred Scripture each day of his life.
Deacons, priests, and bishops are considered clerics, members of the clergy, in the Catholic Church.