What is Sever?

Legal Definition
Practice. When defendants who are sued jointly have separate de-fences, they may in general sever, that is, each one rely on his own separate defence; each may plead severally and insist on his own separate plea. See Severance.
-- Bouviers Law Dictionary
Legal Definition
To separate. When two Joint defendants separate in the action, each pleading separately his own pica and relying upon a separate defense, they are said to sever.
-- Black's Law Dictionary
Legal Definition
To compel or permit one of two or more defendants to plead separately.
-- Ballentine's Law Dictionary