Definition
Available margin is the portion of account resources that remains after current margin requirements and other reservations are deducted from eligible equity.
In market context
Platforms may calculate available margin from account equity, required margin on open positions, pending orders, fees, and internal risk buffers. A positive amount does not guarantee that a new order will be accepted, because instrument limits and post-trade checks may impose additional requirements. Unrealized losses can reduce available margin rapidly and may trigger restrictions, a margin call, or liquidation if required levels are breached.
Risk context
Leveraged positions can consume available margin faster than expected when prices gap or correlated holdings move together.
Source
Use the primary source for fuller regulatory or market context.