Found this on an eBay buying guide:
You may see listed Side steps, Side bars or Running Boards. What's the difference and which one is best for you?
The side bars or Side tube is generally a cosmetic addition to the
vehicle and is not designed for standing. It will generally have a
lighter fixing bracket and is not designed to take any weight. They are
however very handy in car parks and will help to protect against doors
placing those nasty little dents dowen the side of your pride and joy.
The side step is similar in appearance to the Side bar but will
usually be a larger diameter tube and should be fitted with one or two
non slip tread plates.
The fixing brackets will be stronger and are generally fixed using
larger bolts and will support the step from the underside as opposed to
These are ideal if you require assistance entering or exiting the
vehicle, have children or need a step up the roof rails and roof boxes.
They are designed for safe standing and are fully load bearing.
These are another form of step and will use similar fixing methods
to the Side step. The difference being that the Side Step is usually
round or Oval tubing and the Running board is flat and generally made
from an extruded Alloy.
2015 2.2 CDTi SENav 163ps manual 4x4 in Carbon Flash with 19\" alloy spare towing a Bailey Unicorn III Madrid @ 1500kg.