The term Social insects refers to highly socially adapted or "eusocial" species found in the order Hymenoptera and in the termites.  They are characterised by:

a) Living in colonies of a few to many thousand individuals, all genetically identical or very  closely related.
b) Overlapping adult generations, and cooperative care of developing larvae or nymphs
c) Most colony members are sterile non-breeding individuals, with one or a few fertile females (queens) and fertile males often only through part of the year. The genetics of what determines the nature of the adult can be complex.
d) Division of labour with non fertile workers, which may be differentiated into castes such as food gatherer, "soldier" brood-tenders etc, often very different in size and appearance.

Ants, many bees and many wasps are eusocial, some other insects and spiders show degrees of parental care.  While many mammals exhibit social behaviour, only a couple of species, such as the naked mole rat, are truly eusocial.