I call them trestles. Some call them stillage. Other simply call them call them cask stands.
Jeff, in the U.K. at Stonch's Beer Blog, calls them stills —short for stillage. As in, keeping your casks still.
But the crucial aspect of his most recent post is the need to keep casks still, allowing the contents the time to settle, to allow the beer to become clear and free of yeast bite and proteinaceous sludge. Like a keg, the cask needs time after the jostling of delivery for the carbonation to settle down, and return to equilibrium. Translation: you don't want a beer shower when spiling or tapping the cask.
Unlike a keg, a cask contains yeast and protein. Moving a cask re-suspends that sludge into the beer. Plan on a minimum of 24 hours to allow all that to settle beneath the keystone of the cask.
Prepare casks ahead of time.
A pub that sells lots of real ale needs adequate stillage to keep up with demand. Because casks need to be prepped in situ two or three days before dispense, you need at least twice as many stills as you have beer lines.
After delivery of a cask, allow it to sit, cool, undisturbed, on its side, for several days. Do NOT spile it that day. Do NOT tap it that day.
Remember to allow the cask to rise to cellar temperature when it is to be spiled and tapped and served. What's cellar temperature? Think 50 °F or so. If that's not do-able, 'keg' cold is okay, but only if the brewery has already concluded the necessary 'warm' conditioning, before shipping the cask. Ask the brewery.
After spiling the cask, wait for the cask to reach CO2 equilibrium. A rule-of-thumb is fobbing about the soft spile once every 30 seconds or more. Now it can be tapped.
And now wait again. The act of spiling and the act of tapping re-disturb that yeast/protein sediment. Wait a minimum of 24 hours.
To summarize: after putting a firkin on stillage, allow its contents to settle, and then, only after it's been spiled, only after it's come into condition ... then, and only then, serve it, with a smile.