Bread is an uncountable noun. In English, a piece of bread means a piece of bread.
Countable nouns refer to people or things that can be counted in numbers and divided into individuals; Therefore, it has a plural form. When its plural form is the subject in a sentence, the predicate of the sentence also applies the plural form.
Uncountable nouns refer to things that cannot be counted in numbers and can not be divided into individual concepts, states, qualities, feelings or materials; Generally, it has no plural form but only the singular form. It cannot be preceded by an indefinite article. To express its individual meaning, it is generally used with a noun phrase. The meaning of the quantifier in it depends on the collocation with the specific noun. When uncountable nouns use the plural form, their meanings will change. For example, glass is glass and glasses are glasses. Or it generally refers to all similar things, for example, fruit refers to fruit, and fruits refers to (various) fruits. The usage and meaning should be based on the actual situation.