The TETRA Overview page presents some technical information about the TETRA protocol, and touches on some features.
As TETRA was developed in Europe, some of the parts have different names than the traditional US understanding. For example, a Base Station is a transmitter at the towersite, something that US radiopeople may call a Repeater. In TETRA termonology, a repeater is a device that replicates direct mode traffic, and not part of the main trunked radio system.
The TETRA Features page introduces features that are common on TETRA systems. Call modes, Repeaters and Gateways, along with other features, are presented.
The Spectrum page discusses one item of concern: TETRA is a great technology, but where may I find spectrum to license and operate? With the FCC's narrowband mandate, it is important to note that the FCC recognizes TETRA's 25 kHz signal as narrowbanded, as 4 conversations are contained within that one frequency's bandwidth.