Source: /cirosantilli/every-lie-algebra-has-a-unique-single-corresponding-simply-connected-lie-group

= Every Lie algebra has a unique single corresponding simply connected Lie group

This <simply connected> is called the <universal covering group>.

E.g. in the case of <SO(3)> and <SU(2)>, <SU(2)> is <simply connected>, but <SO(3)> is not.