> ## Documentation Index
> Fetch the complete documentation index at: https://doc.lucidworks.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Signals

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[localhost link]: http://localhost:3000/docs/4/fusion-ai/concepts/signals-and-aggregations/signals/overview

[mintlify link]: https://doc.lucidworks.com/docs/4/fusion-ai/concepts/signals-and-aggregations/signals/overview

[old doc.lw link]: https://doc.lucidworks.com/fusion/5.9/469

A *signal* is a recorded event related to one or more documents in a collection. Signals can record any kind of event that is useful to your organization. Click signals are the most common type of signals as this is the most common action a user takes with an item. In addition, other signal types can be defined, such as "addToCart", "purchase", and so on.

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Using a sufficiently large collection of signals, Fusion can automatically generate [recommendations](/docs/4/fusion-ai/concepts/boosting/overview) such as these:

* Based on the user’s search query, which items are most likely to interest them?
* Based on the user’s similarity to other users, which additional items are likely to interest them?

Signals are indexed in a secondary collection which is linked to the primary collection by the naming convention `<primarycollectionname>_signals`. So, if your main collection is named `products`, the associated signals collection is named `products_signals`. The signals collection is created automatically when signals are enabled for the primary collection. Signals are enabled by default whenever a new collection is created.

Signals are indexed just like ordinary documents. The signals collection can be searched like any other collection, for example by using the [Query Workbench](/docs/4/fusion-server/concepts/querying/query-workbench) with the signals collection selected.

[App Insights](/docs/4/fusion-ai/concepts/insights/overview) provides visualizations and reports with which to analyze your signals. App Insights mainly uses raw signals, but also uses some [*aggregated*](/docs/4/fusion-ai/concepts/signals-and-aggregations/aggregations/overview) signals. Currently only the signal types Request, Response and Click are supported within the App Insights dashboards.

See the descriptions of [signals types and structure](/docs/4/fusion-ai/concepts/signals-and-aggregations/signals/types-and-structures) for more information.