Margin call is a broker's warning to a trader that the level of equity in the account is running low relative to the used margin. For example, if the margin call level is 100%, you will get a margin call once Equity / Used Margin <= 100%, i.e. account equity becomes equal or lower than used margin.
You can read more about margin call and stop-out levels here:
https://www.earnforex.com/guides/stop-out-level-vs-margin-call/
Normally, you would want your broker's margin call level as low as possible. On the other hand, a higher margin call level helps careless traders (who
forget to set their stop-losses) to preserve at least a small part of their capital in case of a strong adversary movement in the market.