Quite simply. Static means not moving. if you attempt a push-up and halfway up you hold that position - that portion as a static exercise.

another example is the chair sit. Place your back against a wall and bend your knees as if your sitting in a chair and hold that position - again a static exercise.

they provide some(not much) usefulness in muscular endurance but increases power output and general strength almost not at all.

static stretching involves holding a stretch in a certain position and when not properly performed often results in injury.

isometric exercises are a form of static strength training