Filioque is Latin for "and from the son." This clause, inserted in the Niceno-constantinopolitan creed, has been one point of disagreement between the Western and the Greek Orthodox Church.

".... We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son."

The Filioque clause was inserted in the West at about the 6th century, and has been subject to much bitter debate between the Roman Catholic and the Eastern Orthodox Church, who believe that this is an erroneous addition to the creed.

During the Council of Florence in 1439, the Orthodox Church accepted the Filioque clause, only to retract it in the 1450's. Anglican and Protestant churches generally accept the Filioque clause.

People have suggested that a slight change in the formaulation, from "and the Son" to "through the Son," offers hope for reconciliation among the churches on this matter.


references:
Nicene Creed, britannica.com
Filioque, Catholic Answers