Medium is the general channel type used to describe how traffic arrived, such as organic, cpc, email, referral, or social.
It matters because analytics turns marketing activity into decisions. Without clear measurement language, teams may misread performance, overvalue the wrong channels, or miss the actions that actually drive revenue.
Example
The medium ’email’ can identify how a newsletter visit arrived, while the source identifies which sender or publication supplied it. Consistent naming avoids splitting the same channel between variations such as Email and email.