Users are members with a license giving them access to more features.
It is possible to collaborate in Beesbusy with people who don’t have any license (like for example people outside your organization), and this without limit. In other words, you can collaborate with as many members as you want.
These people will be limited to the “What” view of the projects you will share with them, their Beesbusy account being in free version.
See on this subject the Pricing page describing the perimeter of the accounts according to the kind of licenses.