Flour is a type of powder that is used to make a variety of foods, most notably among them bread.
Flour is a homophone of flower, so flour is pronounced like the word flower.
In fact, flour is a variant of the word flower in English, where both derive from fleur in French. The figurative meaning of fleur was "the finest" and refers to the fine quality of flour.
However, when flour is pronounced with certain British accents, there may be a slight difference between the pronunciation of flower and flour. In these cases, it sounds as if the word flour has nearly one fewer syllable than flower.