Oracle beginner problem, number of connections

what is the relationship between the number of oracle, connections, session sessions and users? assuming that the default number of connections installed is 150, is it true that the total number of connections for all users cannot be greater than 150? Or is the number of connections per user 150? Java connects to the database for operation, is it a connection, or is it a session session? Connect and talk. I"m confused.

Mar.06,2021
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-64f5-1b36c53-2c033.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36c53-2c033.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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