A Smartphone (or Smart Phone, Smart-phone) is a mobile telephone that also incorporates basic functions of a personal computer. This includes gaming, but is not limited to that. Modern powerful smartphones with big screens can easily replace many if not all day-to-day functions of a PC like internet browsing, email, and editing documents. In a way these devices are a fusion of earlier mobile phones and PDAs, that both have become practically extinct.
Note: Since the smartphone market is still very much in flux, the following sections only represents the way things are at the time of writing (2014).
Tomb Raider on Smartphones
The only system that is officially supported by several Tomb Raider games is Apple iOs. (See there for a complete list.) This is mostly due to the pre-defined hardware that is far easier to adapt games to than the highly fragmented Android marked with its dozens of manufacturers and operating system versions. As a result there are no official versions of any Tomb Raider game for the other platforms. (Although there are several attempts to play the old Tomb Raider 1-5 on Android using a PlayStation Emulator - which might be illegal if one does not own such a system and the corresponding game disc.)
For games running natively (without emulation) see the articles about the different Operating Systems: Apple iOs, Google Android
In recent years (since the beginning of the 2010s) smartphones have developed a computing power that previously has not been envisioned. Modern phones feature dual or quad core CPUs and sophisticated GPUs for 2d and 3d accelerated graphics. The majority of these use an ARM architecture, which is power efficient and proven in embedded systems. Almost all modern smartphones are being controlled with a touch screen, a touch sensitive display.
With the trend to bigger and bigger screens, some smartphons now look and feel more like Tablet PCs. These big screen phones are often called phablets.
When in the beginning of the smartphone era Apples iOs was the dominant mobile Operating System, in recent years Googles Android has gained dominance over the market. Blackberry devices on the other hand have almost completely been thrown out, while relative newcomer Microsoft with its Windows Phone line of operating system is slowly gaining momentum.