SEO visibility is a composite score, usually built from a site's rankings across a large basket of tracked keywords weighted by each keyword's search volume, that tries to capture overall search presence in a single number rather than tracking every keyword individually.
Because there's no official standard formula, visibility scores from different tools (Sistrix, SEMrush, and others each compute their own version) aren't directly comparable to each other; the number only means something in the context of that specific tool's own methodology and keyword database. What it's genuinely useful for is trend-watching within one tool over time: a visibility score climbing steadily suggests a site's overall search presence is growing, and a sudden drop is often the fastest way to notice a site-wide problem, an accidental noindex, a bad migration, an algorithm update impact, before it shows up clearly in raw traffic numbers. It's a useful early-warning and trend signal, in other words, not a precise, portable measurement to report as if every tool were computing the same thing.
