An officant is the person that presides over the ceremony. Different denominations have different officiants. Another commonly used term for an officiant is a pastor, in terms of christian weddings and protestant weddings. In Catholic weddings the used term is priest.
There are differences both among the way the ceremonies are performed in other denominations and to whom they are allowed to be performed. Sometimes, this is the key to a couple that has a mixed faith or does not have a faith that they have committed to.
Pastors, will often perform a ceremony for couples that do not belong to the church, where as in a Catholic Wedding, both the bride and groom must be catholic, belong to the church, and under go classes in order to be allowed to have the marriage recognized by the church and performed there. Pastors ,also are willing to perform ceremonies outside of the traditional location of the church. For example, an outside wedding or one at the beach or your own home.
It is important when planning either by yourself or with a bridal consultant to know what type of ceremony you want in order to look at all of your options. For Jewish ceremonies, a member of the community leader may perform the ceremony and not necessarily a rabbi. However if it is performed by someone other than a Rabbi, a civil ceremony will probably need to be done for the marriage to be official and recognized. Also note that a rabbi may or may not perform a ceremony for a couple of mixed faith or to one that does not belong to the synagog. It usually is not done. Muslim ceremonies have an Iman, a spiritual leader in close consultation and the wedding is performed in the mosque. There are many other significant differences involved with the officiants and ceremony procedcures in other denominations and cultures. Its important both as the bride and groom to discuss the options and what is most important to each in the makings of the ceremony. Also, to not forget that for those that want a non traditional small wedding, there is always the option of a civil ceremony performed by a judge of the city you live in.
Picking an officiant can be tough, but remember even if you don't personally know them it is important to remember they will want to make the ceremony a smooth and proud event for you as well as themselves. If you are polite, firm, and able to admit when you are not fully aware of certian aspects of the ceremony they should be compliant and accepting. It is just a matter of showing the necessary respect to them. Some Officiants will be willing to perform a ceremony outside of regular hours such as a monday or a wednesday instead of a saturday or sunday before or after church. Keep the communication cordial and you will not be dissappointed. Good luck and always consider seeking advice or help from a consultant when you are not sure. A little help goes a long way, and can be very affordable.