Microsoft Excel: Macros
Macros can do just about anything you can do in Excel, but are often used to automate a boring, repetitive task.
For example, you may download data from another system into Excel. After downloading the data you may have to tidy it up before you can use it. This can involve deleting irrelevant rows and columns, changing column widths, formatting cells, anything really. But you have to do it every time. If you record a macro you can play it back to have all the steps carried out very quickly.