Clearing members are members of a clearing house, or entity which settles account balances among members, guarantees the other side of all futures trades, and oversees contract performance. Clearing members are also members at one or more exchanges through which they trade.
To guarantee the financial integrity of the futures exchange, a clearinghouse requires clearing members to post a guaranty bond in the form of cash or a letter of credit, which would cover a clearing member in the event of a default. If the money isn't sufficient the clearinghouse can assess a pro-rata levy to cover the difference.
At the end of each trading day, each clearing member's account is marked to market with the closing prices of that day. If additional margin is required of any account, then the clearing member of that account has to post additional margin before a specific time on the next business day.