Q.What is Canonical and Standard Forms?

An algebraic expression can express in two forms:

i) Sum of Products   (SOP) for example (A . B¯) + (A¯ . B¯)           

ii) Product of Sums   (POS) for example (A¯ + B) . (A + B)

If a product term of SOP expression comprises every variable of that function either in true or complement form then it's defined as a Minterm or Standard Product. This minterm will be true just for one combination of input values of variables. For illustration in SOP expression

F (A, B, C) = (A. B.C) +  (A¯ . B¯. C) + (A . B)

We have 3 product terms which are A.B.C, .A¯.B¯.C and A.B however only first two of them are minterm as third one doesn't contain variable C or its complement. And term A.B.C will be one only if A = 1, B = 1and C = 1 for any other combination of values of A, B, C the minterm A.B.C will have 0 value. In the same way minterm. A¯ B¯. C would have value 1 only if A¯ = 1, B¯ = 1 and C = 1 (It means A=0, B=0 and C=1) for any other combination of values minterm would have a zero value.

Similar type of term which is used in POS form is known as Maxterm or Standard Sums. 

Maxterm is a term of POS expression that comprises all variables of function in true or complemented form. For illustration F (A, B, C) = (A + B + C). (A¯ + B¯+ C) has two maxterms. A maxterm has a value 0 for just one combination of input values.  

Maxterm A+B+C will has 0 value just for A = 0, B = 0 and C = 0 for all other combination of values of A, B, C it would have a value 1.