What is the meaning of..........EM

An em is a unit of measurement in the field of typography. This unit defines the proportion of the letter width and height with respect to the point size of the current font. Originally the unit was derived from the width of the capital "M" in a particular typeface. This unit is not defined in terms of any specific typeface, and thus is the same for all fonts at a given point size.[1] So, 1 em in a 16 point typeface is 16 points.