Joint tenants is one of the ways in which property can be jointly held. The co owners own the property jointly. If one passes away their share will pass to the co owners, under the rule of survivorship, i.e. their share will not pass under the terms of their will.
When the property is being transferred, the Transfer must state how the parties wish to own the property. If nothing is stated then it is assumed the property is to be held as joint tenants and not tenants in common.