The Triquetra, Trinity Knot or Celtic Triangle is one of the most common of the Celtic Knots.
There are many theories about the meaning of this popular design, but each one mentions the significance of the three intersecting loops, which, depending on your beliefs, can be interpreted in a number of ways such as Father-Son-Holy Spirit, Mother-Crone-Maiden or mind-body-spirit.
As with the Claddagh, the number 3 represented in the Trinity Knot holds a special connotation within Celtic symbology.