LADA stands for latent autoimmune diabetes in adults. As with Type 1, it is caused by an autoimmune response The immune system targets the bodies own cells. In this case the attack is against the beta cells in the pancreas which produce insulin. This means that eventually the person will produce insufficient and will need to replace that insulin. (ie by injection) In LADA, this can be relatively slow process taking some years.
not needing insulin at diagnosis or for the first 6 months (this one really depends on if someone has ignored/got used to symptoms, there are many people, including myself who get diagnosed at the end of the process and need insulin at diagnosis because of this)
certain antibodies being found in the blood. (most common in LADA are what are called GAD antibodies )
There is a useful chart here showing the differences between T1, T2 and LADA
At the bottom there is also a link to another type of diabetes (MODY) which is occasionally called 1.5
Here is another slightly more academic description. It includes a set of five characteristics of LADA that have been found in some research in Australia (though hasn't been tested elsewhere)