BEM — Block Element Modifier
Blocks, Elements and Modifiers Block Standalone entity that is meaningful on its own.
Examples header, container, menu, checkbox, input
Element A part of a block that has no standalone meaning and is semantically tied to its block.
Examples menu item, list item, checkbox caption, header title
Modifier A flag on a block or element. Use them to change appearance or behavior.
Examples disabled, highlighted, checked, fixed, size big, color yellow