Svchost.exe is a process on your computer that hosts, or contains, other individual services that Windows uses to perform various functions. For example, Windows Defender uses a service that is hosted by a svchost.exe process.
There can be multiple instances of svchost.exe running on your computer, with each instance containing different services. One instance of svchost.exe might host a single service for a program, and another instance might host several services related to Windows. You can use Task Manager to view which services are running under each instance of svchost.exe.