Interpreting deals exclusively with oral communication: rendering a message from one language into another, naturally and fluently, adopting the delivery, tone and convictions of the speaker and speaking in the first person. It should not be confused with translation which deals only with written texts. The job of an interpreter is to enable people to communicate with each other, not by translating every word they utter, but by conveying the ideas which they express. Language regime and active and passive languages are terms used by interpreters to describe the languages you may speak or listen to in a multilingual meeting. An interpreter's language combination describes the number of languages the interpreter works from or into in simultaneous or consecutive mode. There are different kinds of interpreting:
Consecutive interpreting: Interpreting after the speaker has finished.
The interpreter sits with the delegates, listens to the speech and renders it, at the end, in a different language, generally with the aid of notes. In the modern world consecutive interpreting has been largely replaced by simultaneous, but it remains relevant for certain kinds of meetings (e.g. highly technical meetings, working lunches, small groups, field trips). Well-trained interpreters can render speeches of 10 minutes or more with great accuracy.
Simultaneous interpreting: Interpreting while the delegate is speaking.
The interpreter works in a soundproofed booth with at least one colleague. The speaker in the meeting room speaks into a microphone; the interpreter receives the sound through a headset and renders the message into a microphone almost simultaneously. The delegate in the meeting room selects the relevant channel to hear the interpretation in the language of his/her choice. There are many different possible configurations of languages or language regimes.
Relay: Interpreting between two languages via a third.
When a delegate speaks in a language not covered by an interpreter in an active language booth, this booth can "connect" (audio link) to another booth that does cover this language and "take the relay" of that. The interpreter works via another language without a perceptible loss of quality.
Whispering: Whispered Simultaneous Interpreting.
The interpreter is seated or standing among the delegates and interprets simultaneously directly into the ear of the delegates. Whispered interpretation can be used only for very few delegates sitting or standing close together. It is used mainly in bilateral meetings or in groups where only a few delegates do not share a common language. Whispering is often used instead of consecutive in order to save time. Sometimes, the whispering interpreter will use a headphone in order to get the best possible sound from the original speaker.
In addition, types of interpretation are also divided based on the occasion: e.g. business negotiation, tele-conference, IR meeting, IR road show, seminar, trade fair, interview, focus group, assistance for visitors, assistance in hospital visits and shopping trips.
Source: http://ec.europa.eu/dgs/scic/what-is-conference-interpreting/index_en.htm
