Is core on MetaMask?

I'm just curious, could you clarify something for me? I've been hearing a lot about MetaMask these days, and I'm trying to wrap my head around all its features. Now, I'm wondering, does MetaMask include a 'core' component or function? I'm not exactly sure what 'core' means in this context, but I'm assuming it has something to do with the wallet's essential functionality. Could you please elaborate on this? It would be really helpful for me to understand MetaMask better.