A type of aquarium filter that is driven by an electrical impeller. It is completley waterproof and has a media chamber. They are usually small. I've never used one but the main drawback that I can see is that it takes up space in the tank, and they're only good for small aquariums anyways.

The modifier in your head that edits what you say before you say it - especially when you're saying something unfamiliar that requires the application of a rule ie. of grammar or social convention etc.

Used especially in the lingustic context of second language acquisition, where the person learning their second (or subsequent) language must apply a filter to their utterances in order to produce something able to be understood by the listener.