Initial margin is the collateral you must post to open a position. It equals 1 divided by leverage: at 10x you post 10% of notional, at 50x you post 2%. It is the entry ticket, and it is also the maximum clean loss the position can inflict on you in isolated mode.
01What it controls
Initial margin sets position capacity. With $1,000 of collateral at 10x you can hold $10,000 notional. Maximum leverage caps exist per contract, up to 125x on some major perpetuals for small positions, and the cap falls as position size rises through the tiers.
It does not set survival. That is the maintenance margin's job. A position opened at the maximum leverage allowed by initial margin sits a fraction of a percent from liquidation from the first second.
02Initial margin in the liquidation math
Distance to liquidation is roughly initial margin minus maintenance margin. Open at 10x with 10% initial and 0.5% maintenance, and you can absorb about a 9.5% adverse move. That subtraction is the whole reason low leverage survives volatility and maximum leverage rarely does.