What is the FTP Command for deleting multiple files as once?

If you're using the Windows command-line ftp client, then you will need to use mdelete to delete multiple files, as delete will only delete a single file.

Edit: Answering the additional questions in the comments.

If you want to put these commands in a file so that you can perform them as some kind of batch process, you could create a text file and put the commands in sequence there:

prompt
mdel *
quit

Then you could run this as a single step with the -s parameter.

To use mdelete use the syntax below to automate the process

At the FTP> use the "prompt" command to disable interaction (mode off)

Type this command:

• FTP> mdelete [directory] *.extenstion |yes

For example, mdelete standard *.jpg |yes