Precision is the degree of accuracy given for a number or value. Precision is implied by the use of significant figures. A number is given to an accuracy of a number of figures.
The use of implied precision can be a minefield. Spoken numbers need rounding to something like three significant figures; any extremely large or small number should be given in Standard Form.
So what is the number two? It depends on the precision you are using: if working to the nearest whole number, ‘two’ is written 1.5 ≤ 2 <2.5, a half either way.
Standard Form is used to represent large and small numbers in a consistent way. Standard Form shows one non-zero digit before the decimal point and is then multiplied by a power of ten to indicate the size. Thus the absolute number and the general size have been separated. Rounding is carried out as for significant figures (indicated by sig.fig., SF, s.f., Std Fm), and usually Std Fm requires you to think about both the rounding and the power of ten.
The number 3.14 is implicitly 3 significant figures. Setting the value of g to be 9.8 implies 9.75≤g<9.85 but setting g to be exactly 9.8 is extreme precision. This is one way of arguing that two and two might be five; we tend to assume that integers (whole numbers) are given exactly – if they are not, and we assume one significant figure instead, then two values of say 2.3 add to sufficient to total more than 4.5, and hence round off to five when expressed to only one significant figure.