Chairman
Chairperson, Speaker
noun
The person in charge of long discussions is the chairman, or the speaker. They also say who gets to talk and for how long.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
議長は危機をだっしました。
The chairman got through the crisis.
あのバスの最後尾の席に座っている黒いスーツの男性が議長です。
The man in the black suit sitting in the last row of the bus is the speaker.
私がこの会議の議長を務めさせていただきます。
I am acting as chairperson of this meeting.