Tangible fixed assets generally refer to assets that have a physical value. Examples of this are your business premises, equipment, inventory and machinery. Tangible fixed assets have a market value that needs to be accounted for when you file your annual accounts. Some of these assets, for example computer equipment, will incur depreciation, which needs to be factored into your accounts.
The opposite of tangible assets are intangible assets, such as patents, trademarks and copyright. These all have an intangible value as they usually have little value to anyone outside of the business.