TLDR:

Semi-colon (“;”) to end DML statements and Forward Slash (“/”) for DDLs.

Now, below is a great article, that explains the reasons and the history of confusion on Oracle SQL termination symbols:

• https://www.codeproject.com/Articles/702974/Oracle-Forward-Slash-in-SQL-Plus-Take-2

P.S. Having both ; and / may lead to double-execution in SQL*Plus