Interpolation means you are estimating a value which lies between two known points. Thus, if you are measuring length with a meter stick and the line is between 41 and 42 cm, you interpolate or estimate the value to be about 41.5 cm.
An electronic scale is accurate to some given level, which is usually stated on the instrument. If you get a reading of 100. 5 grams and the instrument is accurate to the nearest gram, that actually means that the value is somewhere between 100 and 101 grams. If the instrument is accurate to the nearest 0.1 g, then the value is between 100.4 and 100.6 grams. So an electronic scale is in effect interpolating and then displaying a single number which in effect is its best "guess" of the mass of the object.