Wikipedia
Apparentment is the name given to the system, sometimes provided for in elections conducted according to the party-list proportional representation system, which allows parties to specify electoral alliances. The system has been used in Switzerland since 1919.
In list PR systems, seats are awarded for each quota of votes obtained. Any votes excess to the quota are lost. Under apparentment, parties combine their vote excess, which may yield an additional full quota and candidate elected.
There are two possible types of apparentment: different parties within a single electoral district combining their results, or the same party competing in different electoral districts combining these results.
The system introduces an element of ordinality. It is akin to a pre-specified ranking in a preferential voting system like Alternative Vote or Single Transferable Vote, as is used with the above-the-line system in Australian elections.