Session is a group of user interactions with a website or app during a defined period of activity.
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
A person can view a service page and a contact page during one visit. Those interactions may belong to one analytics session under the configured rules; they should not automatically be interpreted as two different prospective customers.