Every time you tap a link to open a Web page in Safari on your iPhone or iPad, it automatically opens a new tab. That’s fine until you realize that you have oodles of old tabs open, making it difficult to find any particular tab. To close all your old tabs in one fell swoop, press and hold on the tab button, then tap Close All X Tabs in the popover that appears.
Cleaning these up won’t make your device run any faster because these tabs aren’t loaded into memory if you haven’t used them for a few minutes. But if you dislike clutter and you’re finding it difficult to locate the things that are useful to you this could be easier than closing all of them one-by-one.