This term has a number of meanings:
In the context of security, a charge (www.practicallaw.com/A34644) over a particular asset where the chargee controls any dealing or disposal of the asset by the chargor. A fixed charge ranks before a floating charge (www.practicallaw.com/A36124) in the order of repayment on an insolvency.
In relation to a tenancy, under the Landlord and Tenant (Covenants) Act 1995, rent, any service charge as defined by section 18 of the Landlord and Tenant Act 1985, any amount payable under a tenant covenant (www.practicallaw.com/A34765) of the tenancy providing for the payment of a liquidated sum in the event of failure to comply with such a covenant.