If you have permission to add or update assets you will see a link 'Update Items' in the left-hand menu.
If you click on this option, you will notice that there are two update functions:

• Batch Update - Performing a batch update enables you to search for assets to create a selection to work on, then step through each asset, one at a time, to update its metadata. So for example, if you wanted to add descriptions to all assets in a particular category, you would use Batch Update to complete this (as each description will vary from asset to asset).
• Bulk Update - In a Bulk Update, you again start by searching for assets to create a group of items to act upon. You can then define changes or additions to the metadata which will be applied to the entire group of assets in one operation. So for example, if you wanted to move assets from one category to another, you would use Bulk Update to apply the change to all these assets in one go (as stepping through each one individually and making the change would be inefficient).