That is, what is included in a report, the type of report written, and the organization of a report are determined by the situation that gives rise to the report. Short reports and those that are standardized don't require a great deal of special arrangement of the material. However, longer reports or special reports must contain elements that require special attention. Not all reports contain all of these elements. You must decide which to include by the context and situation in which you are writing and by your reader's needs.
Reports also summarize the conclusion of a research or other type of project.
Finally, reports can be short or long, formal or informal. Quite often, reports have a transmittal memo or letter that identifies the report and explains the key points. The memo or letter can also describe the situation that gave rise to the report. Reports and their transmittal documents are often separated as they travel from reader to reader, thus need to be redundant. Some readers will only read one section of your report, so each section must be complete.