A vacuum cleaner, or sometimes a hoover, is a machine that is used to suck dirt and dust from floors inside your house. It works by making a vacuum inside it by pumping the air out of a chamber inside the cleaner, so that air from outside rushes in to fill up the space that is left. The dust is removed from the air by filtering it, usually through some cloth.
Valerian is a hardy plant with pink or white flowers. The roots of the plant can be used for medicinal purposes, usually by making them into a tea. Valerian has a sedative effect and helps you to sleep.
You may also be interested in red valerian, an unrelated plant with a similar name.
Vampires are a mythical creature which is said to exist by drinking people's blood. They are said to only come out at night as daylight can destroy them. It is also said they can only be killed by a stake through the heart, or by a silver bullet. A vampire has no reflection, so they cannot be seen in a mirror.