what is "local block" in pg_stat_statements? https://www.postgresql.org/docs/9.4/static/pgstatstatements.html

local_blks_hit  bigint      Total number of local block cache hits by the statement
local_blks_read bigint      Total number of local blocks read by the statement
local_blks_dirtied  bigint      Total number of local blocks dirtied by the statement
local_blks_written  bigint      Total number of local blocks written by the statement


Doc says "local block" and where does it point to??
From https://www.postgresql.org/docs/9.4/sql-explain.html:


  Shared blocks contain data from regular tables and indexes; local blocks contain data from temporary tables and indexes; while temp blocks contain short-term working data used in sorts, hashes, Materialize plan nodes, and similar cases.