What does it mean to expand a node?

I'm trying to understand the algorithm for a Depth-Limited-Search on wikipedia, and I'm trying to figure out what exactly it means to expand a node. I attempted to search for an answer but all I got was more algorithms which state that nodes must be expanded.

Specifically, what is the line stack := expand (node) saying in regards to the whole function?

    DLS(node, goal, depth)
    {
       if (node == goal)
         return node;
      push_stack(node);
       while (stack is not empty)
       {
         if (depth > 0)
         {
           stack := expand (node)
           node = stack.pop();
           DLS(node, goal, depth-1);
         }
           else
           // no operation

      }
     }