Speyside is home to over half of Scotland's Malt Whisky distilleries, not all of which are open to the public. The Malt Whisky Trail is a local marketing initiative (theme route) established to promote the region's Whisky heritage and encourage tourism.
The trail itself is well-marked at the roadside at various points and the distilleries can be visited in any convenient order. Some are popular with coach parties, but others are more esoteric. A tour of Cragganmore for example requires prior booking via the Cardhu distillery visitors' centre.
There are many more Speyside distilleries not on the trail, and many allow visitors to tour the production areas. However, the trail makes a good starting point.