Pro-Rata Rights
An investor's right to invest again in later rounds to maintain their ownership percentage.
Pro-rata rights let an existing investor put money into future rounds to avoid being diluted. An investor with 10% can buy enough of the next round to stay at 10%.
For investors this is where much of the return in a winning company is captured — the right to keep buying into something already working.
For founders it constrains later rounds. If several early investors exercise pro-rata, there may be little room left for the new lead a Series A requires. Worth modelling before granting the rights widely.