Event Parameter

An event parameter is an extra piece of data sent with an event that describes its context — like the payment method sent with a purchase event.

An event parameter is what turns a raw event into analyzable data: without one you only know a purchase happened, with one you know which product, at what amount, in what category. A subtle but important distinction: an event parameter holds the context of that moment's action and attaches to the event itself, whereas a user property sits on the profile and persists; confusing the two leads to wrong reports. The second trap is unique-value explosion: a parameter whose values are effectively unbounded (like an exact transaction id) is useless for grouping and only bloats the table; a good parameter has limited, meaningful values. The word parameter is more common in GA's vocabulary, while event-based tools call the same thing an event property.