Vote pending closure just means that a vote for such things as deletion or policy is currently being won by one of the sides, but that the required time has not yet been passed for the vote to be considered closed. This criteria will vary depending on the type of vote, so see the relevant policy:

According to the deletion policy one page must maintain a specific lead for a number of consecutive days in order to win. The {{Delete/Closing}} template can be added to the page to notify others that there are enough votes to win and vote is waiting on the time period to elapse before the voting is over. A vote does not have to be marked as pending closure for the vote to close. You can still vote during this period, which may indeed cause the vote leave the "pending closure" state if you're voting against the currently winning side. Deletion votes pending closure can be found in Votes for deleting pending closure.

According to the voting policy one page must maintain a specific lead for a number of consecutive days in order to win. The {{Vote/Closing}} template can be added to the page to notify others that there are enough votes to win and vote is waiting on the time period to elapse before the voting is over. A vote does not have to be marked as pending closure for the vote to close. You can still vote during this period, which may indeed cause the vote leave the "pending closure" state if you're voting against the currently winning side. Regular votes pending closure can be found in Votes pending closure.