Triage shows you your new emails, internal notifications and mentions from colleagues.
Only you have access to your own Triage. Your colleagues however, may have access to emails that are shared on timelines.
Emails can be shared by:
Assigning the email to a colleague
Sharing your emails for that contact.
You will know if as well as how many of your colleagues are able to see an email by looking at the information tray of the email under 'Visibility'—this lists any colleagues who have access to the email.