He or she is called a conductor. By conducting, the whole orchestra has something to focus upon, someone to refer to in terms of speed, expression, volume, length, and pauses. It is entirely possible for an orchestra to have no conductor. If I am not mistaken, one such orchestra is called the Orpheus Orchestra (correct me if I'm wrong, guys!). They played just as good as any other orchestra that has a conductor.
https://answers.yahoo.com/question/index?qid=20080304234402AAdmHJV
Description[edit] Modern batons are generally made of a lightweight wood, fiberglass or carbon fiber which is tapered to a comfortable grip called a bulb that is usually made of cork, oak, walnut, rosewood, or occasionally aluminum and that may be tailored to a conductor's needs.
https://en.wikipedia.org/wiki/Baton_(conducting)
Valery Gergiev is another conductor who often does not use a baton. His technique was on display at a rehearsal of the London Symphony Orchestra at Avery Fisher Hall in preparation for a performance of Mahler’s Symphony No. 3.
http://www.nytimes.com/2012/04/08/arts/music/breaking-conductors-down-by-gesture-and-body-part.html
Traditionally (for right-handers, at least), the right hand holds the baton and keeps the beat. It controls tempo — faster here, slower there — and indicates how many beats occur in a measure. The baton usually signals the beginning of a measure with a downward motion (the downbeat).
http://www.nytimes.com/2012/04/08/arts/music/breaking-conductors-down-by-gesture-and-body-part.html
The stick held by a conductor or Maestro (an endearing term of affection for great conductors) is a baton. Below are a few links describing some conductors, their techniques, some that use batons, some that don't, and even a Woman's successful attempt to shatter the glass podium. Hope this helps.
https://answers.yahoo.com/question/index?qid=20080304234402AAdmHJV
An upward movement prepares for the downbeat. Conducting manuals say the upbeat and downbeat should take the same amount of time, and that interval should equal the length of the beat. “The upbeat is the preparation for any event,” said Alan Gilbert, the music director of the New York Philharmonic.
http://www.nytimes.com/2012/04/08/arts/music/breaking-conductors-down-by-gesture-and-body-part.html
The usual way of holding the baton is between the thumb and the first two fingers with the grip in against the palm of the hand. The baton is usually held in the right hand though some left-handed conductors hold it in the left.
https://en.wikipedia.org/wiki/Baton_(conducting)
Some conductors prefer at times, or all the time, not to use a baton. Yannick Nézet-Séguin, who becomes the music director of the Philadelphia Orchestra in September, is one. His training came mostly with choirs, for which batons are rarely used.
http://www.nytimes.com/2012/04/08/arts/music/breaking-conductors-down-by-gesture-and-body-part.html
In the end it must be remembered that the art of conducting is more than just semaphore. It is a two-step between body and soul, between physical gesture and musical personality. The greatest technician can produce flabby performances. The most inscrutable stick waver can produce transcendence.
http://www.nytimes.com/2012/04/08/arts/music/breaking-conductors-down-by-gesture-and-body-part.html
Before the use of the baton, orchestral ensembles were conducted from the harpsichord or the first violin lead. Conductors first began to use violin bows or rolled pieces of paper before the modern baton was introduced.
https://en.wikipedia.org/wiki/Baton_(conducting)
what is a conductors white stick called
The white stick of a conductor is called Baton. A white stick of conductors is called a Baton.