Fixed Restraints that keep the subject in a standing position (or nearly so). This doesn't include restraints where the subject is upright but not standing, for instance when hanging, kneeling, sitting, or on a rotated slab. Use Upright Restraints in these cases.
With restraints, the subject is often supported in some way, but to merit this tag they should have their feet on the ground and could theoretically be supporting their own weight if not for the restraints.
If the subject's feet can't be seen, but it can be reasonably inferred that they are standing, use this tag.
If the character is Standing, but the restraints aren't keeping them that way, that doesn't count as standing restraints. An example would be a character standing while their arms and legs are tied. Since they could sit down (or fall over), they aren't actually restrained to a standing position.