It's called a clothes line. What you do is you connect a piece of string between two points so that it is taught and then you put wet clothing on it. This can be done inside or outside and it saves you a bunch of money as well as lowering your carbon footprint since you don't need the materials for a dryer or the energy that it takes to run the machine. There are also a bunch of other advantages to your clothing by line (for example your clothing won't shrink).
I don't know the official figures about Spanish clothes line use but anecdotal evidence suggests that a majority of Spaniards use them, my host mother is no exception. It's a bit cold outside so it takes a while for everything to dry and there is only so much space on the line so you the load size is kind of small but that's fine with me since it lowers my carbon footprint. It's funny how higher energy prices are leading us back to simpler times and back to devices we used to use for hundreds of years and the whole thing about the simplest solution is often the best one.