A historically significant price level that price action has had a difficult time trading below.

If price action drops and approaches a confirmed support level, a re-test of support occurs and it can be either confirmed again or broken.

A test at support is confirmed if a bullish change in the market sentiment occurs at the support level. 

Support is broken when the bearish market sentiment does not change at the support level and price action continues down through the support level.

Support once broken become resistance.