The difference between a theorem and a conjecture :-
Theorem :- Something which is true and can be proved .
I am giving a very simple example here .
Angle sum theorem :- sum of all angles in a triangle will be equal to 180° .
This is a theorem because every interior angle of a triangle will add up to 180° . It cannot change .
So , something that is definitely true and can be proved is a theorem .
Conjecture :- Something that is supposed to be true , but still hasn't been proved to be true .
Example :-
1a = 10
2a = 20
3a = 30
With this you can guess that 4a must be equal to 40 , but it can't be proved without using algebra .
Therefore , something which is likely to be true is a conjecture ( in maths ) .