In Forex, a market lot is the minimum amount of units for trading.
A standard lot consists of 100000 units. There are mini, micro and nano lots too.
Forex lot size is as follows,
Standard lot: 100,000 units
Mini lot: 10,000 units
Micro lot: 1000 units
Nano lot: 100 units
Which size of a lot will you trade? It depends on your investment size.
If you have $100, then you should trade larger than micro lots. Forex market will not stop you if you trade in the mini or standard lot, but it carries enormous risk to do that.
If you want, you can trade 1 mini lot with $100 as Forex market allows high leverage. One thing you should remember, the higher the leverage the higher the profit and risk.
Excessive leverage will lead you to a margin call sooner or later if you do not choose a lot size properly. We will discuss margin call later.