In Star Trek, these are fields which can be set up nearly anywhere on a starship. They are permeable to light and sound, but impermeable to solid objects and energy weapons. There are varying levels of force fields. I'm not sure what they correspond to in terms of strength / square meter, or if that sort of measure even applies to these things. They are invisible until they are touched, at which point they light up around the point of contact and seem to discharge a little static onto the person / thing which contacted it.