This isn’t about periscopes or mouthwash—when it comes to searching, a scope is the area in which a search takes place. When you use the Search field in a Finder window to look for files and folders, you have the choice of two scopes: This Mac or the current folder. You can always switch the scope after starting the search by clicking the other choice near the top of the window, but it’s easier to set the default search scope in Finder > Preferences > Advanced so it’s set right to start. From the “When performing a search” pop-up menu, choose Search This Mac to search across all indexed drives, Search the Current Folder to limit the search to the folder showing when you start the search, or Use the Previous Search Scope. Most of the time, if you have any idea where the item you’re looking for might be, selecting an enclosing folder and then searching within it is the best approach.
Apple’s Photos app on the Mac can identify thousands of different objects in your photos, so it’s easy to find photos based on their content. You can find objects (cars and trains), scenery (beaches and forests), and even some events (weddings and parades). This is both big fun and useful for those times when you can’t remember when you took a photo, but do remember what’s in it, like a cat, camera, or carousel. To carry out a search like this, type the search term into the Search field on the right side of the Photos toolbar. From the list that appears, choose the Category result. In macOS 10.13 High Sierra’s version of Photos, you can filter your results from the Showing menu at the upper right of the window. The feature isn’t perfect, so you may see some odd results or miss some photos, but it’s way faster than browsing manually!