Share of voice
Your slice of the total attention in a defined set of competitors, over a defined window.
Share of voice is your portion of the total measurable attention across a named set of accounts in a named time window. If you and four competitors collectively earned a million views last month and you earned two hundred thousand of them, your share of voice is twenty percent.
Three things decide whether the number means anything: who is in the set, what metric you're totalling, and how long the window is. Change any one and the number moves. That is not a flaw as long as you hold them fixed and track the trend, which is the only way share of voice is genuinely useful: the level is arbitrary, the direction is not.
Watch for a dominant outlier. One account that vastly outproduces everyone else will hold most of the share by definition, which makes everyone else's number look like noise. When that happens the honest read is usually "we are competing for second place in this set", not "we have four percent of the market".
Where this comes up
Your slice of the attention in a defined set: how to compute it from public data, and why the level is arbitrary but the direction isn't.
A repeatable method for reading a competitor's strategy from public data alone: what to collect, how to compare it honestly, and what it can't tell you.