Every photo you take with your iPhone has metadata attached to it - information about the photo like what camera it was taken with, the coordinates where it was taken, date, time and more. You can add data as well, including a title, description and keywords to facilitate search results. The Photos app is able to detect faces, and if there are any faces in a photo that you have assigned names to, and the app recognizes them, then those names will be in the metadata as well.
The Photos app is seemingly improved with each new iOS, and this holds true with iOS 12 as well. In addition to improving the search function (allowing you to search by place or event and multiple keywords), allowing for editing RAW files, and an overhauled Albums layout, Photos in iOS 12 adds a For You tab that includes a number of features. Here's an overview of the new For You section:
iOS devices offer a quick way to hide specific pictures in the Photos app. Hiding photos simply places them into a Hidden album, and removes the images from elsewhere in the photo library. While this provides iPhone, iPad and iPod touch users with an easy method of hiding pictures on the Camera Roll or another album, these images can be viewed directly in the Hidden album at any time.
Those who are signed up for Apple's Beta Software Program and testing iOS 12 may have noticed that it offers a new way to share photos - by sharing a direct link to your iCloud Photos that will last for 30 days. Not all features found in beta make it to the official iOS, but hopefully this one will, as it pretty useful for sending multiple photos. Instead of actually attaching each photo to an email or sending them in Messages, you are merely posting a link.
Having an iPhone with a nice camera and plenty of storage coupled with an album that lives in the cloud rather than on the device can lead to having an enormous amount of photos. This is especially true if you are the type that takes many shots of the same subject while planning on deleting all but the best one later, which invariably results in hundreds, if not thousands of duplicate photos taking up space on your camera roll.