What it is
People confuse static caravans with touring caravans because they look alike. They are not travel vehicles: they are moved a couple of times a year at most, and in many European parks they are permanently sited.
Why people choose it
In the UK and Ireland, statics are governed by the Mobile Homes Act and sit on licensed sites under site licences. On the continent they are usually subject to construction standards and planning permission. Check the local rules before buying.
What to check before you buy
For an RV traveller the practical point is simple: if you want to move once a week, this is the wrong category, and you should be looking at a touring caravan or a motorhome instead of a static.