The track on a railway (non-US) or railroad (US), also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast (or slab track), plus the underlying subgrade. For clarity it is often referred to as railway track (British English and UIC terminology) or railroad track (predominantly in North America).
1- Ballasted Track
Notwithstanding modern technical developments, the overwhelmingly dominant track form worldwide consists of flat-bottom steel rails supported on timber or pre-stressed concrete sleepers (referred to as railroad ties in the US), which are themselves laid on crushed stone ballast.
Most railroads with heavy traffic use continuously welded rails supported by sleepers (ties) attached via baseplates (tieplates) which spread the load. A plastic or rubber pad is usually placed between the rail and the tieplate where concrete sleepers (ties) are used. The rail is usually held down to the sleeper (tie) with resilient fastenings, although cut spikes are widely used in North American practice.
Timber sleepers (ties) may be of hardwood or softwood, and are customarily treated with creosote or other wood preservative. Pre-stressed concrete sleepers (ties) are often used where timber is scarce and where tonnage and/or speeds are high.
The track ballast is customarily crushed stone, and the purpose of this is to support the ties and allow some adjustment of their position, while allowing free drainage.
2- Ballastless track
Rail traffic is reaching out toward new horizons on ballastless track systems. The arguments are indeed convincing: long life cycles, top speed, ride comfort, and great load-carrying capability. You take no chances with these systems, especially with newly constructed lines: even at speeds over 300 km/h, your coffee will stay in your cup. Practically maintenance free, ballastless track systems ensure almost 100% availability over many years. In many cases, a maintenance-free track system is indeed the more cost-effective solution over the long run.
Source: wikipedia.org, railone.com, “Simply supported composite railway bridge: a comparison of ballasted and ballastless track alternatives” by Guillaume Gillet, railway-fasteners.com