A filter is something that lets some things pass through it, but stops other things. Filters are found in many places. When you make coffee, you use a filter to stop the solid parts of the coffee from getting in the liquid part that you drink.
The filters in the picture are a clean and dirty air filter. The filter on the right is full of all the dirt and grime that has been stopped from going through the filter.
Filth is disgusting, dirty waste. You might also use filth as an insult, for example "you people are all filth".
Finches are small, seed-eating songbirds. They come in a huge variety of colours and patterns, and can be found all over the world. Many finches are very pretty and make good pets.
