From OpenStreetMap Wiki
|barrier = hampshire_gate|
|A section of wire fence which can be removed temporarily.|
|Used on these elements|
|Tools for this tag|
is a section of wire fence which can be removed temporarily.
How to Map
Simply add the tag barrier=hampshire_gate to a node where the gate is.
You should also add further tags to more fully specify what kinds of vehicle or foot traffic have reasonably unhindered access using access=*.