The term commonly used for an Elven marriage vow, between two partners referred to as trothmates.
However, Elves regard pledging differently than mortal species such as humans, Chakka or Warrows. Since they are immortal, they do not pledge to remain together for the rest of their lives. Instead, pledging is a potentially temporary union, which bids them only to stay together for as long as their destinies require and as long as they have "common ground." No pretense of permanency is included in their vows.
It is typical that if a pair of lovers have gotten to the point of pledging that they will remain together for a long time. Occasionally a pledged pair will go their separate ways. For instance, Faeon was originally the trothmate of Eiron. However, after the death of their son Galarun, they parted and she instead became pledged to Inarion. There seems to be no formalities for dissolving a pledge; the partners simply cease their relationship.
A pledging is primarily a speech given by a high-ranking Elf in front of a large crowd of witnesses, which explains the nature of the pledge to the trothmates. After that, there is a celebration.