The tools used in businesses to create results are usually considered to be computer related these days. An example of a software program that can help with project management is a word processing program that allows multiple form letters to be created where only the specific information about the individuals that will receive the form letter are changed within the letter. The result will be many letters printed out while only one letter had to be written or typed.
Project management does not, however, always need to use a computer related tool to complete a task. An example of this is when mail is received each day at a company. The tools could include a person with a date stamp performing the needed activity of sorting and stamping the mail.
So the tool will vary depending upon the product that needs to be produced under the guidelines of project management. Many times the tool ends up repeating a task in a repetitious pattern such as date stamp used in manual labor or a printer with multiple copies of the same type of letter. Either way, the tool used, will have completed the task and produce the needed results.
This term is defined in the 3rd and the 4th edition of the PMBOK.