Op is asking that question in the Trading Discussion board, meaning he is referring to the chart since traders always use it.

Supply defines as sellers. Supply zone is where a sellers put their orders so when the price reaches that zone it will bounce back.

Demand defines as buyers. Demand zone is where buyers put their orders so that it will bounce back when the price hit that zone.

Order Block is also known as supply/demand. In a smaller time frame, an order block can be viewed as a consolidation of candlesticks followed by an impulsive candlestick.