Investment is the expenditure by businesses on new capital over some period and saving is income which is not spent by households over the same period. Both investment and saving are related to the interest rate. Investment is negatively related to the interest rate.
Investment is business spending on new capital.
Higher interest rates raise the cost of acquiring new capital, while lower interest rates reduce the cost of acquiring new capital. Businesses must expect that the rate of return from buying the new capital will be greater than the interest rate they must pay to finance the new capital. At higher interest rates, fewer investments meet the expectations criteria. At lower interest rates, more investments meet the expectations criteria. Therefore, businesses will invest more when interest rates are low and less when interest rates are high.