I've encountered several clients recently who seemed to be conducting meetings where board members were making decisions but unit owners were not notified of the meeting and were not invited to attend.
It's important to understand that ANY meeting of the board where decisions will be made and action taken must be open to all unit owners. While owners do not vote on the matters at hand during a regular board meeting, they do have a right to observe the proceedings.
Board members can share information and discuss the issues that will be voted on at the meeting prior to the actual meeting, but whenever a decision is made that vote must be officially recorded in an open board meeting. (The only exception would be where emergency action must be taken in order to address damage to the units or common elements or potential injury to the owners.)
The IL Condo Act requires at least 48 hours' notice of a board meeting. Your By-Laws may show a different requirement. More about meeting notices here.
Certain topics should not be discussed in an open portion of a meeting. See a previous post on this.