The latter; the second of two (or more) items previously mentioned.
提案Aと提案Bがあったが、私は後者を支持する。
There were proposal A and proposal B, and I support the latter.
前者は安価だが品質に不安があり、後者は高いが信頼できる。
The former is cheap but has quality concerns; the latter is expensive but reliable.
A successor or descendant — someone who comes later, such as an heir or descendant (used in the sense of successor/descendant).
家督を継ぐのは後者であることが家族会議で決まった。
It was decided at the family meeting that the latter would inherit the household headship.
先祖の意思を継ぐ後者は、地域の伝統を守っている。
The descendant who carries on the ancestor's will is preserving the local traditions.