Outlook’s search box is a powerful tool to help you find messages, contacts, tasks, and calendar entries. You can type a number of phrases in the Search box at the top of the Outlook window. In addition to searching for different words and phrases, you can use various operators and keywords to narrow your search results. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.