What are called the standard conjectures on algebraic cycles are several conjectures brought up by Grothendieck, concerned with the relation between algebraic cycles and Weil cohomology theories.
In as simple terms as possible, the Hodge conjecture asks whether complicated mathematical things can be built from simpler ones.
Not so dissimilar to seeing an entire working city built from Lego and realising that it is in fact all just made from little simple square blocks.
The Hodge conjecture is a major unsolved problem in algebraic geometry that deals with the structure of harmonic forms on algebraic varieties.
It states that the cohomology classes of algebraic varieties that are represented by harmonic forms are precisely the classes that can be represented by algebraic cycles.