Each time you access a file through your web browser, the browser caches (stores) it. By doing this, the browser doesn't have to newly retrieve files (including any images) from the remote web site each time you click Back or Forward. You should periodically clear the cache to allow your browser to function more efficiently.

A cookie is a file created by a web browser, at the request of a web site, that is then stored on a computer. These files typically store user-specific information such as selections in a form, shopping cart contents, or authentication data. Browsers will normally clear cookies that reach a certain age, but clearing them manually may solve problems with web sites or your browser.

A browser's history is a log of sites that you visit. When you use a browser's Backbutton, you are moving back one entry in the history log. Browsers will normally clear the history at regular intervals, but you may want to clear it manually for privacy.