There are multiple definitions - click on the translation that matches your context.
guaranteed permanent employment, especially as a teacher or a lecturer etc, usually after an initial trial period
We've abolished security of tenure for any newly appointed staff.
the guaranteed right to occupy or hold a building, land, or other real property, usually for a specified length of time
The Contract is conditional upon the superior landlord's consent being granted and also the parties obtaining a court order to exclude the security of tenure.