does boxing mean only one character at a time, or only one period?

[Oyster Hippopotamus]

hello, sorry for my noobish question, this is my first time playing Everquest, i did not play back in the day and I have not played the full version of EQ either, so I am slightly confused about the boxing rule. does boxing mean we can only have one character active at a time, or only one character period? If it's the latter, I guess that means there is no way to play all the different possible character combinations? Or, you would at least need to delete your existing character first?