Half Life is the original game released in the late 90's. This also include the popular multi-player mod Counter Strike.'Source' is the name of the new game engine that was designed to run it's...
Shelf life: Time that something (e.g. food, batteries) can stay good in storage, unused (aka on the shelf). This is a rough estimate that depends on various conditions (e.g. temperature, humidity)....
As long as the Half-Life games makes Valve some money, they won't change a winning recipe. So, there will almost for sure be another Half-Life game. yes the first half life was a great success and so...