Exposure

Depending on how much you invest in a particular investment, you are said to be exposed to that investment.

For instance, if 90% of all your savings are invested in the stock market, then you would be "overexposed" to the stock market. Or, if you have just 5% of your investments in the stock market, you are "underexposed" to the stock market.

The same principle holds when investing in different countries.
An international investor may not want to invest all his money in one country (overexposure to one country) but will prefer to balance his investments (exposure) amongst a few countries.