Closed list describes the variant of party-list proportional representation where voters can (effectively) only vote for political parties as a whole, and thus have no influence on the party-supplied order in which party candidates are elected. If voters have at least some influence, then it is called an open list.
In closed list systems, each political party has pre-decided who will receive the seats allocated to that party in the elections, so that the candidates positioned highest on this list tend to always get a seat in the parliament while the candidates positioned very low on the closed list will not.
However, the candidates "at the water mark" of a given party are in the position of either losing or winning their seat depending on the number of votes the party gets. "The water mark" is the number of seats a specific party can be expected to achieve. The number of seats that the party wins, combined with the candidates' positions on the party's list, will then determine whether a particular candidate will get a seat.