Aluminium slat fence runs flat or shaped aluminium extrusions horizontally between posts. Slats are typically 65 to 150 mm wide, fixed to posts via screw-on brackets or by sliding into a channelled post. Steel posts (galvanised SHS) are common for strength, with aluminium slats fixed to them. All-aluminium versions use thicker walled aluminium posts.
The big appeal is low maintenance. Powder-coated aluminium doesn't rust, doesn't rot, and goes 15 to 20 years before colour fades. Compared to a slatted steel fence, the aluminium version is lighter, easier to install, and cheaper per metre at most spec levels.
Downsides: aluminium dents more easily than steel, so a low-mounted slat takes damage from kicked balls and trolley bumps. And aluminium slat is not always pool-compliant unless the brackets and spacings are checked against AS1926.1.