Tubular fence is a generic term for any fence built primarily from steel tubes. The most common pattern is a 50x50 SHS top and bottom rail with vertical 25x25 SHS bars between them, all welded into pre-fabricated panels and bolted to SHS posts.
Tubular fence is the workhorse of Australian residential security and pool fencing. It's cheaper than a custom slatted or battened panel fence, holds up to weather (galvanise + powder coat), and the open structure passes wind without acting as a sail.
For pool compliance, vertical bar spacing must be 100 mm or less (AS1926.1) and the top rail must not be climbable from outside. Most modern pool fence panels are tubular fence variants designed to AS1926.1 from the start.