In the New Testament Presbuteros means "elder", and refers to the custom of choosing leaders and advisors from among the wisest members of the church.
The Presbyterian church is a representative democracy governed by elders elected from and by the congregation.
Authority resides with the duly elected representatives of the congregation in the appointed church governing bodies. The local church governing body is the session.
Local sessions oversee the day-to-day work of the church and supervise:
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deacons -- elected to conduct the temporal and charitable ministry of the church
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trustees -- (in some churches) elected to manage financial, legal and property affairs of the church
Including the session the overall church structure consists of four governing bodies:
The session consists of ordained ministers (ministers of the Word) and elders -- all elected by the congregation. Elders and ministers from congregations who oversee the local churches are the Presbytery.
The Synods are representatives elected from each Presbytery to oversee several Presbyteries.
The national governing body made up of equal numbers of lay people and clergy chosen by the Presbyteries is the General Assembly.