Gap
Gaps form when opening price movements create a blank spot on the chart. This occurs when the high of the day is below the low of the previous day or when the low of the day is above the high of the previous day. Gaps are especially significant when accompanied by an increase in volume.
Gap - Breakaway
Breakaway gaps signal a potential change in trend and are especially significant when accompanied by an increase in volume. A bullish breakaway gap forms when a security gaps up after an extended decline. Bullish breakaway gaps can also occur after an extended base or consolidation period. A bearish breakaway gap forms when a security gaps down after an extended advance. Bearish breakaway gaps can also form after an extended top or consolidation period.
Gap - Common
Common gaps occur within a trading range or shortly after a sharp move as a reaction. These gaps do not signify the beginning or continuation of a move, but rather represent anomalies. For instance, if a security has declined 20% in a week and gaps up, it would be considered a common gap and not likely to signify a change in trend. Or, if a trading range develops between 20 and 30, and a gap forms in the middle, it is probably a common gap.