Only incoming data that meets a filter's rules count as tasks. If incoming data that triggers a Zap doesn't pass the filter, it does not count as a task, and will not count against your monthly task limit.
If you have multiple filter steps in a Zap, each filter step that allows incoming data to pass through counts as a task. For example, if you have two filters in a Zap, and incoming data passes the first filter but not the second filter, one task will be counted.
In Zap History, filter steps have the status Filtered if the incoming data did not pass the filter and the Zap run was stopped, and the status Successful if the incoming data passed the filter and the Zap run continued.