The technical specification lays out the requirements for the project, AKA project design document. It contains great details of the project, such as screen shots, menus, and a detailed description of the purpose of the project. A project could consist of multiple programs which all work for some common purpose, wuch as Windows Office and Open Office. Both these projects contain multiple programs. The author(s) of such technical specifications may find that it is necessary to split it up into multiple specification documents, such as one for Word, another for Excel, etc.
What will the documents contain? As I already mentioned they will contain as much detailed information about the project as humanily possible. If I come to you and ask you to write a program to help me manufacture widgets then you will write the technical specs to make sure that both you and I agree on what the program will look like and how it will behave. Without such agreement the project will probably fail or will cost you a lot more money then I paid you because you will have to re-write the parts that were not previously clarified. And if I come back again and ask for more changes the previously agreed upon technical specifications will give you justification to ask for more money to pay for the new requirements.
Finally, the technical specification is the document that the programming staff will use to write the program(s).