Gate Passage in the Slalom next, or page 1

A gate has been passed correctly when both the competitors’ ski tips and both feet have passed across the gate line. (661.4.1) 

The gate line in Slalom is the imaginary shortest line between the turning pole and the outside pole. (661.4.1.2) In the illustrations that accompany this section, the gate line is depicted as a dashed line. The only purpose of the outside pole(s), is to serve as a point of reference for where the line begins and ends on the surface of the snow. In and of themselves, the gates (poles) are not meaningful. Only the gate line is meaningful, as it serves to identify the zone of correct passage. 

In Slalom, the two poles comprise a gate as only two pole are required to define a gate line. In Slalom, the colors of the gates (pole pairs) alternate. They are usually red and blue, although other colors may serve. In Slalom it is no longer required, as it once was, that flags be affixed to the ends of the poles. It is at the discretion of the Jury. Slalom is unlike Giant Slalom, Super-G, and Downhill in that only single poles are used at each end of the gate line.