What are SLR digital cameras?
SLR stands for Single Lens Reflex which is a camera in which the user sees exactly what the camera sees through a series of prisms and mirrors. Interchange of lenses is possible that is a great feature for photographers. These offer high resolution but do have significantly high cost.
 
What is lens aperture?
Lens aperture is the ratio of the focal length of the lens to the diameter of the light rays passing through the aperture in the iris diaphragm. F-number settings are adjustable. Lens aperture is also called f-number.

Is there any difference between optical and digital zoom?
There is a zoom lens in optical zoom as it would be in a traditional camera. If you want a picture that is three times closer than the basic image, try out camera with an optical zoom of 3X.
 
Digital zoom is a digital technology that takes a real optical image, and then "zooms" it. Blowing up each pixel does this and also interpolation is used for the same. Digital zoom mostly results in an instant decrease in an image's clarity and sharpness.

Is it advisable to do filtering when it comes to motion stuff?
It is best NOT to use a filter if it is not absolutely necessary for example to polarize for shooting flat work. This is because of the reflectiveness of the imaging sensor.
 
How has the Parallax Error been eliminated in Digital SLR Cameras?
Parallax is the phenomenon by which the shorter the distance between the subject and the camera, the greater the angular error in the actual and the perceived image. In most SLR cameras, settings can be controlled manually, which allows an individual to get a good shot in fast action with an unusual focal plane. But some digital SLR cameras do have automatic focus.