The same size fraction can be written using different numerators and denominators.
e.g. 4/8, 10/20, 3/6, 5/10 & 1/2, are all the same size of fraction, they all represent a half. These are all equivalent fractions.
If we multiply both the numerator and the denominator of a fraction by the same integer (whole number), the result is an equivalent fraction.
Similarly if we can divide both the numerator and denominator of the fraction by the same integer (whole number), to produce new integers for both the numerator and denominator, this is again an equivalent fraction.
In the first examples that we looked at, e.g. 4/8, 10/20, 3/6, 5/10 & 1/2.
1/2 is the lowest form of expressing these equivalent fractions. We can tell this from the fact that there is no number other than one, which can divide evenly into both the numerator and the denominator.
If there is no integer greater than 1, that can divide evenly, into both the numerator and the denominator of a fraction, then the fraction is in its lowest form.
Other examples of fractions in their lowest form. 2/3, 5/7, 1/3, 3/22, etc.