What is a foo.1 file?

Hello All,

A cron job caused an update query to run out of resources. This morning, looking
for any needed cleanup, I found a file I don't recognize. The file tbl_voters_full
is a table involved in failed query, but not the table being updated. The file
tbl_voters_full.1 is new to me, and it does contain data. Is this a temporary table?
Is it safely deletable?

** snipped from a ls of /home/postgres/data/base/pacwebdev
-rw------- 1 postgres postgres 1073741824 Oct 4 23:53 tbl_voters_full
-rw------- 1 postgres postgres 144687104 Oct 5 00:09 tbl_voters_full.1

Thanks for your help,
David Huttleston Jr