If your company practice team selling, you can enable Opportunity Team in Salesforce from Setup | Customize | Opportunities | Opportunity Teams | Opportunity Team Settings, then select Enable Team Selling.
When running an opportunities report, you have several choices in the standard filter area that allow you to choose what types of records should be searched. Once Opportunity Team Selling feature enabled, you will have additional options when running Opportunity report.
This is options available before enable Team Selling
This is options available after enable Team Selling
The list below identifies what each choice means and how it affects the scope of your report data:
ONLY the opportunities you OWNED.
My team-selling opportunities:
ONLY the opportunities where you are on the SALES TEAM.
My team-selling and my own opportunities:
Opportunities OWNED by you & opportunities where you are on the SALES TEAM.
My team's opportunities:
Opportunities OWNED by you & users who report to you in the role hierarchy.
My team's team-selling and their opportunities:
Opportunities OWNED by you & users that report to you in the role hierarchy, ALSO opportunities where you & users who report to you in the role hierarchy are on the SALES TEAM.
ALL opportunities visible by the user who run the report.
Note: When Opportunity Split enabled, opportunity owner will be automatically added into Opportunity Team with role = Opportunity Owner, read this blog.
Reference: Opportunity Reports: Opportunity Team Selling