Scrims are a little similar to barn doors as they attach in front of a light source in the filter frame. A scrim may cut the light completely or part of it or graduated across it. Half scrims are available to cut half of the light. A scrim can cut the light's intensity without altering any other aspects of the light, such as its color. Scrims come in various sizes and shapes and are usually made of black metal foil or wire.
Larger frames such as butterflies and overheads are often used to hold materials like silk and diffusers away from the lights. Small circular scrims on a handle are called dots. They are usually clamped relatively close to a light and can be opaque or partly opaque. They are typically about 2-10 inches in diameter.
Small rectangular scrims are called fingers and are used in the same way as dots. You can also get bags and cases for scrims. Most lighting kits include scrims or you can get them separately. They can be bought from about $5 each.