The sample statistic which we use to estimate population parameter is called point estimate. Because we use single sample statistic to make estimate about population parameter . It gives particular single value which we can use as estimate of population parameter, hence it is called point estimate.
Ex: Suppose we have population mean and we use sample mean to find estimate population mean. Then Population mean is called parameter, sample mean is statistic. And as we have used sample mean as estimate of population mean , sample mean is called as point estimate.