"Sidekick" can refer to a few things, depending on the context :

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A helper or assistant:

This is the most common meaning. A sidekick is someone who accompanies and assists a main character, often in a less prominent role. Think Robin to Batman, or Ron Weasley to Harry Potter. This can be applied to any context, not just fictional characters.

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A specific product or service:

There are various products and services that use the name "Sidekick," often implying a supplementary or supportive role. These could be software tools, apps, or even physical products. Without more context, it[SQ]s impossible to say which specific "Sidekick" you[SQ]re referring to. Examples might include a CRM sidekick, a social media sidekick, or a fitness sidekick app.

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A type of character role in fiction:

In storytelling, the sidekick is a recognizable character archetype with specific traits and functions within the narrative.

To understand what *your* "Sidekick" is, you[SQ]ll need to provide more context. Where did you hear or see the term used?