A sponsored account (sometimes referred to as a sponsored user or sponsored membership) is a special membership that is paid for by a main account holder.
In most cases, a main account holder would be the employer/manager of an organisation, and a sponsored account holder would be an employee or volunteer from the same organisation.
Sponsored users have the same privileges as a normal account (individual username, login details, device allowance, saved videos etc). The only difference is that membership payments are billed only to the main account holder.
If a main account holder cancels their subscription, then all of their sponsored members will lose access to the video library too.