1. A penetration of an enemy's defense in depth and strength.
2. Making an important discovery.
3. A crack or break in a filter bed allowing the passage of floc or particulate matter through a filter. This will cause an increase in filter effluent turbidity. A break- through can occur: 1) when a filter is first placed in service, 2) when the effluent valve suddenly opens or closes, and 3) during periods of excessive head loss through the filter (including when the filter is exposed to negative heads). break through
4. An important discovery or development that solves or eliminates a problem that is preventing you from doing something is a breakthrough.

1. When you use force to go through a wall or other barrier, you break through it.
2. When you cannot do something because of a problem and you find a way to solve or eliminate the problem, you breakthrough.