What's the difference between .sock and .pid?

I found php-fpm.pid :
in the / var/run/php-fpm/ directory, but I couldn"t find the php-fpm.sock file. Where do I usually store it? And what"s the difference between them?

May.14,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3b7f6-2baef.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3b7f6-2baef.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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