If a committee does not act on a bill, it's the same as if they would have voted it down.
When a bill is introduced in the Congress, it is referred to a committee, where they, as an essential part of the legislative process, have the chance to examine it carefully and determine whether it passes or not to the next step. However, if the committee does not act on the bill, the bill is "dead", which it's the same as they have voted it down.
