The last digit in any number is referred to as the estimated digit. In science, all other numbers are considered significant digits because they are precise measurements.
The last number in a measurement in science is simply an estimation. For example, if a metal rod measures slightly over 234 inches, the final measurement can be rounded so the answer is 234 instead of 234.2. The more significant numbers a digit has, the more precise the measurement. A significant number includes all non-zero numbers, all zeros that fall between two significant digits and all zeros that are to the right of a decimal point or to the right of a non-zero number.