'Joint tenancy' is one of two ways of owning a property jointly.  The other way is 'tenancy in common'.  The expressions are a little confusing because they have nothing to do with rented property.

A couple who own their property as joint tenants own the property jointly on the basis that if one of them dies the other automatically becomes the sole owner of the property.  The share that had belonged to the deceased accrues to the survivor.  This is known as the 'right of survivorship'.

Most married couples own their home as joint tenants, but some are tenants in common.  If you are unsure which you are, the best way to find out is to check the legal document which transferred the property to you when you bought it.  In nearly every case this will be Land Registry form TR1.  If you do not have a copy of the document one can be obtained from the Land Registry or possibly from the firm of solicitors or conveyancers who acted for you in the purchase.