Filter

The system that cleans the sucked-in air before returning it to your home.

HEPA filter

A high-efficiency particulate air filter that screens the air the vacuum expels. A HEPA filter can remove allergens down to those 0.1 micron in size (that's smaller than bacteria). HEPA filters cost from $20 to $80, and most HEPA vacuums require at least an annual replacement. They are said to be helpful for people who have asthma or are allergic to dust.

Amps

The amount of current the vacuum draws. Amps indicate the strength of the motor, which does not always translate into greater cleaning power.

Watts

The amount of electricity used. As with amps, wattage is not necessarily related to cleaning power.