"To fix a term" means to establish or set a specific duration or time period for something to happen or be valid. It is like making a decision or agreement about how long something will last or be in effect. Full definition
The changes provide for fixed terms of between one and six years. (humanrights.gov.au)
Bonds are debt instruments with fixed terms of repayment and with fixed interest payments made during the life of the bond. (smallbusiness.chron.com)
This is a 6 month fixed term contract with the possibility for this to eventually go permanent at some stage however this is not guaranteed. (cv-library.co.uk)