Striking off or dissolving a company means that its name is simply removed from the Register of Companies. Once a company is dissolved, it no longer exists.
This is an informal process and whilst a company no longer exists, it can be reinstated in certain circumstances (for example, where a creditor can demonstrate that a company has actively failed to pay them).
An informal striking off of a company is only successfully available where all debts have been cleared. It can therefore be a useful process for companies with no debt and a small level of assets. For companies with no debt and larger levels of assets, it is often more tax efficient to follow the formal process of an MVL, to secure the current beneficial tax rates.