A Deputation

1. The act of deputing, or of appointing or commissioning a deputy or representative; office of a deputy or delegate; vicegerency.
2. The person or persons deputed or commissioned by another person, party, or public body to act in his or its behalf; a delegation.
3. The general sent a deputation to the enemy to propose a truce.
4. Among Christian missionaries, the process or period of time during which they raise support in preparation for going to their mission field.

The use of the word in the missionary sense has been common in churches and mission organizations for over a century, but has recently been giving way to the more "bureaucratic" term "home ministry assignment". As commonly used, a missionary does deputation or is on deputation. However, the missionary is not called a "deputy" nor is the person said to be a part of a "deputation". Deputation begins when the missionary is officially commissioned to be a missionary, and it ends when the person goes to the mission field.