eDiscovery and content search has been a staple of Microsoft 365 compliance since the early days of Office 365. Providing extremely flexible and efficient searching and actioning of data that resides anywhere in Microsoft 365, it has improved over time with a lot of extra functionality and is one of the most widely used compliance tools in the Microsoft 365 platform.
eDiscovery, which has first found in the Exchange Online Admin Center for mail discovery, was subsequently moved to the Microsoft 365 Security & Compliance Center (https://protection.office.com). The Security & Compliance Center itself has undergone a lot of changes recently and is coming near its end of life, being replaced with the Microsoft 365 Security Center (https://security.microsoft.com) and the Microsoft 365 Compliance Center (https://compliance.microsoft.com) which cater to Security tools and Data Governance/Compliance tools respectively.

The splitting of the SCC into two different portals makes sense as a lot of the time, in enterprise scenarios, these aspects of the tenancy are managed by two, completely separate teams. There will often be a dedicated security team, who deal with the identity protection and security aspects of the tenancy, and a dedicated Data Protection Team who are more concerned with the information governance side of things.
As of Oct 30th 2020, the eDiscovery suite of tools will be moving fully to the Microsoft 365 Compliance Center and the Security & Compliance Center links will redirect to the new page. This is the next step in the process of moving all the features from the old portal to the new model so if you haven’t checked out the two new pages, see below for more information.
Microsoft 365 Compliance Center: https://docs.microsoft.com/en-us/microsoft-365/compliance/microsoft-365-compliance-center?view=o365-worldwide
Microsoft 365 Security Center: https://docs.microsoft.com/en-us/microsoft-365/security/mtp/overview-security-center?view=o365-worldwide
Direct links:
SCC: https://protection.office.com