In a general sense presiding officer is synonymous with chairman.

Specifically, Presiding Officer is the title of the post of Speaker in the following legislatures:

• Presiding Officer of the National Assembly for Wales
• Presiding Officer of the Northern Ireland Assembly
• Presiding Officer of the Scottish Parliament
• Presiding Officer of the United States Senate

Other uses of the phrase include:

• Presiding Officer (ARB) is the officer in charge of one of the Administrative Review Boards run by the United States Office for the Administrative Review of Detained Enemy Combatants, at the Guantanamo Bay detention camps, in Cuba
• Presiding Officer (Guantanamo Military Commissions), the officer acting in a judge-like role for Guantanamo Military Commissions.