A continuous weld runs the full length of a joint without breaks. It's the strongest version of any joint geometry and the default whenever the joint is structural, weather-sealed, or visible.
For gate work, every mitre corner, hinge plate, drop-bolt receiver, and footplate weld should be continuous unless there's a specific reason to stitch. Continuous welds also seal the joint against moisture ingress, which matters for hollow sections being galvanised after fabrication: water trapped inside an unsealed joint can flash to steam in the galvanising bath and cause a spectacular failure.
On a 50x25 RHS mitre corner, a 4 mm continuous fillet around all four faces of the tube section is the standard call.