Baiting for termites has a long history.  I first used it in 1979 to survey a park, but others had used baiting way before then.  Basically, a bait is something that termites will happily eat.  Often it is placed in a fancy (=expensive) container.  When the termites are feeding on the bait you (i) know they are there, (ii) can identify them and (iii)  you can exploit them.  The original bait box method had the termites collected and dusted with toxin before being allowed to sulk home.  Other methods replace the actual bait with one containing a slow-acting toxin.  If done well, the toxins applied can spread through the colony before any individual termite is affected and so, with luck, the whole colony will die.

Baiting is good for colony control and sometimes for monitoring but it typically does not provide any residual protection and baits don’t equal a barrier. There’s lots more information here.