The logo is one instrument; identity is the orchestra
If a logo is the signature, a visual identity system is the entire handwriting — the complete set of visual elements that, working together, make your business recognizable at a glance. It includes your logo, but also your colors, your typography, your photography style, your icons, and the rules for how they all fit together on a page.
The reason it has to be a system and not just a logo is simple: your brand shows up in dozens of places — your website, your social posts, your signage, your invoices, your vehicle, your emails. A logo alone can't carry all of that. But a consistent palette, a recognizable typeface, and a distinct image style can make every one of those touchpoints feel like they came from the same place, even when the logo isn't front and center.