MonoHybrid- It is a cross between 2 indivisual having one pair of contrasting trait. e.g. Aa with Aa
Diyhybrif- IT is cross between 2 indivisual having one pair of same allel e.g TT with tt
Test cross- It is cross between f1 generation and one of the parents(recessive ) 
back cross-Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent.

1) mono hybrid cross :- it is a type of cross in which one characteristic is crossed at a time 
2)di hybrid cross:- it is type of cross in which two characteristics are crossed at a time 
monohybrid = cross in which only 1 pair of contrasting charecters are involve dihybrid = in which 2 contrasting charecters are involve
test cross= cross between F1 gaenaration individual with its 1 of rececive parent back cross = F1 hybrid with 1 of any parent