When a status is showing as "pending" next to an approver's name for a requisition, the requisition is waiting on action from the approver. The approver needs to take action on the requisition by either approving or denying it.
Open: When a status is showing as "open" next to an approver's name, this kind of means the approver is on deck. In other words, the approver before them has to approve the requisition before it gets to them.
Approved: The requisition has been approved to an order.
Denied: The requisition has been denied by the approver. The requester either needs to submit a new requisition or resubmit the requisition with any possible changes.