Silly question regarding Backup types 1

[patloner]

I really should know this, however, the terminology being used in the Microsoft courseware is very confusing. Just to make sure I want to post this question. Here is a quote from the Microsoft courseware:

"Transaction log files are not deleted from the server at the completion of an incremental backup. As with the full backup, transaction log files are purged from the server at the completion of an incremental backup of a
storage group."

Can someone explain to me the difference between deleting the transaction log files and purging them from the server. Are these not basically the same thing? Thanks

 

[xmsre]

Transaction logs contain transactions that may or may not yet have been committed to the database. Purging them commits all the transactions to the database. Truncating the logs at the end of a full online backup not only commits the transactions [purges] but deletes the log files containing only committed transactions [truncates].