A patent application comprises the documents sent to a Patent Office to start the patent application process. In the UK the minimum content required at the first step – and in order to be able to claim that you have a “patent pending” – is a formal request for the grant of a patent, a description of the invention with the necessary drawings, while a European application must also include one or more claims. This is necessary because the EPO will conduct a search as soon as you file an application, and they need to know what you are claiming as being your invention. In practice most patent applications in the UK and Europe will include a description, claims, abstract and drawings unless it is being filed in the absolute minimum period of time and there is time only to submit the minimum necessary information to gain IPR.
Further or revised documents may be added to the initial application later, although the precise rules vary in different jurisdictions.

A patent application also refers to the document that the Patent Office publishes to let all interested parties know that you have applied for a patent and what is being claimed for the new invention. This Patent Application is almost universally published eighteen months after your first filing. The US Patent & Trade Mark Office (USPTO) refers to a “Patent Application Publication”.

You can make a patent application on your own behalf, but it is more normal to use a patent attorney. The process is not only procedurally complicated, but the value that your patent will ultimately have depends on the quality of the patent specification that is written and the negotiations with the examiner as it goes through the prosecution stage.